Luigi & Sonic: Dimension Tension (also known as Luigi & Sonic RPG in Japan and South Korea, and Luigi & Sonic: Dimensional Combo in Europe and Australia) is a turn-based role-playing game that depicts a crossover between the Mario series and the Sonic the Hedgehog series. The game is based on the Mario & Luigi series of role-playing games, but features the brother of Mario, Luigi, teaming up with Sonic and new faces from across the Toadstool Earth and Mobius Black as both are threatened by villains from the Cidimension, Alcoberta, Hol-e and the Chompagne Clan. It was released for the Nintendo Switch on October 14th, 2017.
In a dark, hostile dimension between the rift that divides all universes, a high-security prison is broken into by a young, pint-sized girl with a large flower on her back, followed by a group of bun-shaped monsters. Using a pack of locust-like explosives with drills in their legs, she busts out a demented outlaw, who looks like a bat and goblin hybrid, from a tight, robust cage. Together, they escape from security easily with the hybrid's reality warping powers. They disappear into a dimensional portal, but they're pursued by a fast-moving creature wearing detective gear.
On Toadstool Earth, in the peaceful Mushroom Kingdom, Mario and Luigi are having lunch at their house, exchanging heroic tales. Polterpup appears to warn the Mario Brothers of something dangerous outside. When they step out the front door, they're welcomed by two of the bun-shaped monsters. They attack, only to be beaten easily by the combined efforts of the brothers. This opportunity is used to get back into practice on their battle skills.
Afterwards, they find out the castle of Princess Peach is under attack by a new malicious force. On their way over, they bump into Bowser and his Koopa Troop. They happened to be on their way to kidnap the princess once again, but they were beaten to the punch. Before they can get into a skirmish, a tornado of bubbles starts swirling around the area. As bubbles with captured people, including Peach, rise out of the castle, it is destroyed by a gigantic laser shot from an unnatural, rainbow-coloured storm cloud. Other bubbles manage to catch Bowser, the Koopa Troop, a bunch of Toads, and even Mario. Luigi, putting all his strength into running away, dodges the bubbles, but is chased by that devastating laser. Out of nowhere, before he's caught in the destructive light from the sky, a portal opens in the green man's path.
Luigi is passed out, but when he comes to, he finds out he's still alive and, thankfully, safe from danger. The fast moving detective creature appears before the shaken plumber, explaining the situation. He tells Luigi that a wicked practitioner of reality warping magic from the Cidimension, named Alcoberta, has crossed over from his homeworld with the intent of devouring joy, love and virtue from worlds such as Toadstool Earth. He then says that the villain's accomplices are Hol-e, a poison loving little girl, and the Chompagne Clan, a ferocious force of bun-shaped monsters, including the ones that fought the Mario Brothers earlier. The detective, finally, informs Luigi that he is no longer in the Mushroom Kingdom, but on the world of Mobius Black. His first suggestion is to seek out Lord Sonic the Hedgehog, believing him to be the help required to take on a threat as powerful as Alcoberta. The direction of Lord Sonic's castle is pointed out on the MultiWorld Map, given to Luigi by the detective before they part ways.
Luigi travels across the mountainous region of Mt. Oak Nut before reaching Hedgehog Castle, where Lord Sonic rules. Upon entry, he's backed up against a wall by an orange two-tailed fox, Commander Miles "Tails" Prower, a red echidna with spiked fists, General Knuckles the Echidna, and a purple cat, Chief Blaze the Cat. They see Luigi as an intruder trying to usurp the Lord. Luigi tries to explain, but they refuse to take his word for it. Luigi is brought to Lord Sonic in chains, who is revealed to be a disgruntled, caustic, thuggish monarch. He demands to battle with Luigi to make him suffer for the crime he never meant to commit. The hedgehog and his terrified prisoner have a battle, where the former manages to gain the upper hand by utilizing a powerful crown that shields him from every strike and makes his own attacks far more potent.
Before it ends in complete tragedy, the quick stranger shows up to break up the clash, even cancelling out Sonic's crown enhancement. Vouching for Luigi on the situation, Sonic continues to be cynical on the matter. Just then, the castle is struck by the Chompagne Clan and the storm cloud that hit the Mushroom Kingdom. Everyone gazes out the window, where they witness that enormous laser, hitting Sonic's country at full force. The bubbles reappear as well, capturing civilians from all across the nearby area. Sonic finally listens to reason and decides to have the castle evacuated. Their next course of action is to take Sonic's aerial cruiser, the Zoom Typhoon.
When the Zoom Typhoon gets into the air with Luigi and company on it, everyone reflects on what transpired. Luigi is broken, lamenting over how everyone he held dear is captured, and probably even dead by now, and the fact that Sonic is such an unpleasant sovereign to Mobius Black. When asked by the detective about how he behaves, Sonic refuses to go into detail. Realizing he hasn't properly introduced himself, the detective reveals his name to be Zipop, the Lightning Streak of Justice. He discloses his mission to travel across dimensions and prevent Alcoberta from causing destruction across parallel worlds. He appears to be able to open portals, but his reality bending powers are nowhere near Alcoberta's level. Just when things are settling down, another aerial cruiser bumps into the Zoom Typhoon.
Getting a good look from the upper deck, Sonic recognizes the enemy cruiser as the Egg Carrier, a vessel created and controlled by his old nemesis, Dr. Eggman. Sonic is bewildered, having believed for a long time that his eternal enemy was defeated for good, but the all-too-familiar voice of the devious scientist is heard over a loudspeaker. Challenging the bad doctor, the Egg Carrier dispatches a legion of Badniks into the Zoom Typhoon, forcing the crew onboard to go on the offensive. Luigi, Sonic, Zipop, Tails, Knuckles, Blaze and the castle guards do battle with the Badnik swarm. Luigi and Sonic fight their way out of the Zoom Typhoon and infiltrate the Egg Carrier. When he realizes Luigi's desire to help defeat a common enemy, Sonic reluctantly joins the green plumber. When they get to the top of the Egg Carrier, Eggman is nowhere to be found. A giant, hound-shaped Badnik comes out for a battle, facing defeat at Luigi and Sonic's teamwork.
Eggman scoffs at the Egg Greyhound's defeat, boasting about greater things in store. Luigi and Sonic's are then stopped by the sudden appearance of Alcoberta and his right-hand lady, Hol-e. They display bubbles with Tails, Knuckles, Blaze and all of Sonic's castle guards trapped inside. The dark, reality rending hybrid vows to drain all the soul energy from their bodies until they're dry. Sonic tries to attack him head-on, but he is swiftly countered by an energy knife. Alcoberta leaves Luigi and Sonic for Hol-e to play with. Hol-e poisons the two with venomous needles protruding from her fingers and deploys giant locust bombs above the Egg Carrier and the Zoom Typhoon. Sonic admits that Luigi was helpful while the partnership lasted, while Luigi bawls his eyes out over his loss. Zipop intervenes by pouncing Hol-e, but she retaliates with her flower, attaching it to Zipop and spinning in like a buzzsaw, making him dizzy to the point of immobilizing him.
Luigi, remembering Mario, realizes how much he would want his brother to tough it out. Despite his poisoned condition, he gets up and lifts the worn down Sonic into his arms. He tries to get Zipop as well, but it's hopeless with both arms full. Hol-e gleefully kicks Luigi while he's trying to change his fate, but the moustache bearing hero keeps on moving. Hol-e, having had her fun, tries to catch Luigi and Sonic together with a single bubble, but miraculously, Zipop recovers from his dizziness and takes the shot as Luigi continues his attempt to get away. Hol-e disappears with the apprehended Zipop as the bombs finally hit the Egg Carrier and Zoom Typhoon. Luigi jumps off the Egg Carrier and falls a great distance out of the sky as colossal explosions devastate the great airships.
Luigi and Sonic land in a lake near a mountain village, falling unconcious. They come to in a house, watched over by a woman with a notepad tied around her neck. Sonic realizes that he and Luigi are now in the Guffalps, a populated mountain area that celebrates the joy of laughter. The woman introduces herself as Verity, the Truth Chaser. She claims to have come from the Rice Archipelago on Toadstool Earth, but appeared on Mobius Black recently thanks to a key-shaped item. Sadly, the item was taken away by the leader of the village, Shoguffaw, after some accidental collateral damage, and she's been tasked with community service ever since. Sonic goes out for a run while Luigi explores the village, talking to the natives. He walks up to a palace at the peak, where he gets the chance to meet Shoguffaw, who turns out to be a large fire belly newt.
Sonic joins up with Luigi right after the meeting; this perturbs Shoguffaw, as he sees Sonic as a threat. Unhappy that the despotic hedgehog was cared for in his village without his consent, he sends out his army of Giggleishas and Snickurais to assault them. Luigi and Sonic run away, managing to find a shortcut out of the village with help from Verity. After fighting their way through enemies, Luigi and Sonic find a cave with a river in it, only to be stopped by Shoguffaw. They defeat him, earning his praise over how well synchronized the two are in their moves. Luigi remembers to ask about the key-shaped item that Verity mentioned, and the beaten newt leads them to the depths of the cave where he brought it after confiscating it. When they find it, Luigi picks it up and, with a couple of twists, the key opens a dimensional portal.
Sonic is reluctant to go through, knowing that Alcoberta is still out there on Mobius Black, but Luigi is more than willing to return home and help his world fight off the rising threat. Luigi convinces Sonic to come through the portal, betting that Alcoberta will be waiting for them, wherever they go, so there'd always be a chance to get back at him. With that, it's off to Toadstool Earth they go. Verity stays behind to continue her service to Shoguffaw.
Meanwhile, on a bat-shaped airship, Alcoberta is discussing his plans to his victims, claiming that there's an extra layer to the absorption of everyone's life, then hinting at a mole helping in his operation. He sets the airship to make a dimensional jump over to Toadstool Earth to check on the construction of his grand fortress, Moonshine Citadel. Everyone he's captured is inside an organic looking machine, trying desperately to escape. Inside that very machine, at that moment, a tiny, blue, mechanical purple sprite comes in and breaks as many prisoners as it can out of their bubbles before falling down from exhaustion. Mario, Princess Peach, Zipop, Captain Toad, Toadette, a pink hedgehog named Amy Rose and a cream coloured rabbit named Cream the Rabbit are set free. The robot sprite, after an energy boost from Peach's magical touch, introduces itself as Mochiwinkle, a robot created by Professor M. Pestle.
Introductions are cut short when an emergency fail-safe built into the machine activates. Mochiwinkle and all the freed captives are force to flee. Mario and Amy manage to fight their way through Chompagne soldiers and lead everyone to an exit. Mario sends Amy and the others through an escape chute one at a time, just as the airship arrives on Toadstool Earth. Before he can follow behind them, the red hero is recaptured by Hol-e, who admires the attempt at a daring escape, but has to stress that orders from the boss are not to be disregarded. She takes Mario back to his confinement in the machine, telling him that defeat is a healthy learning experience.
Luigi and Sonic come out of the portal to the sight of a beautiful place where nature and technology harmoniously co-exist. They walk into a nearby town where friendly rabbit-like people live. Instinctively, they explore and say hello to the townspeople. Two of these are a kindly male rabbit named C. Pestle and his jolly daughter, Sagi, who have come around to visit the great Professor M. Pestle. The green man and blue hedgehog are lead to a tower-like building in the middle of town, where the rabbit professor lives. It's revealed that C. Pestle is the professor's son, thus making Sagi the professor's granddaughter. The old rabbit happens to be exceptionally proud of his work, because he knows well he has breached all technological walls. He lets Luigi and Sonic know that they're on the Rice Archipelago, the island of perfect synchronization, and the town is Rabbabite Burg.
Luigi asks about Verity, to which the professor replies that he knows her as a friend of his son's. Happy to know that somebody who's knows the family, he lets Luigi look through a telescope that shows the wide area around the town. He sees a dark, electrified cloud of fog where Princess Peach's Castle and Toad Town are supposed to be. Knowing that this could only be the work of that Alcoberta character, Luigi asks the professor if he's seen any bun-shaped monsters. Just then, Rabbabite Burg is placed under attack by those very bun-shaped monsters, the Chompagne Clan. Luigi and Sonic rush outside to see the devastation going on. Mochinwinkle arrives to report where the monsters are coming from. They need to go down south and find the source at the Shiitak Mines.
The duo makes a timely arrival at the mines, as they see a mass production plant has been established here under everyone's noses since the Chompagne Clan arrived on Toadstool Earth. Before Luigi can think too hard about how long he's been gone, Sonic tells him to pick up the pace. On their journey through the mines, they learn how to drill into the ground and how to spring up to otherwise unreachable heights with their very first Combo Actions, in the midst of fighting through hordes of monsters. At the bottom of the mine, they find a machine that's turning seed-like objects into more of those bun-shaped menances, and the one supervising the operation is a larger bun-shaped beast with a blubbery appearance. Sonic goes about smashing the machine, which angers the fat monster. Surprisingly, he seems capable of speech, unlike the rest they had seen up to this point. He announces himself as Private Chomprum, the youngest of the Chompoid Brothers, three of Alcoberta's toughest enforcers. He lets out a battle cry before starting a fight. He loses, resulting in his retreat and the mass production plant's termination.
Out of the machine comes another one of those keys. However, unlike the other, it doesn't seem to work. It's taken back to M. Pestle for examination. The professor takes a good look at both of Luigi and Sonic's keys and comes to two conclusions. One is that the new key is cut in half. Without it's other half, it cannot function. Second, a complete key, like the older one, is locked to certain locations on Toadstool Earth and Mobius Black. There's no telling where they may end up if they find the second half of the second key. Before he lets them go, M. Pestle gives the man and hedgehog duo a Key Case to hold a keys in, and some new clothing to equip. As they head up north, the broken key starts radiating a light that points toward another part of the Rice Archipelago. They end up going on for a while, fighting enemies along the way, until they reach another town by some high hills.
Luigi and Sonic are welcomed by a friendly Chain Chomp to Wasab Valley, a place where creatures known to be enemies of the Mario Bros. have found tranquility. At least they were tranquil until a gigantic monster started attacking the valley, making them live in fear. Houses have been devastated, playgrounds built with M. Pestle's technology are destroyed and many of the residents were eaten for all three meals of the day. The Chain Chomp introduces himself as Chainling, a peculiar member of his species who has learned to use his chain as an effective weapon and support appendage. Suddenly, the monster appears, prompting everyone to duck for cover. Luigi, Sonic and Chainling aren't spotted, but the colossus inhales some vegetation and more of the valley's people. It flies away afterwards. Chainling joins the man and animal duo as they make their way toward where the beast flew off to.
On the way up the hills, they spot a figure wearing a trenchcoat. The figure questions the three about their motivations. Luigi says he was sent up to this point by a signal emanating from his cut-in-half key. Sonic says he was brought along for a chance to get at Alcoberta. Chainling says he wants to meet the monster and find out why it's hurting everyone in Wasab Valley. The figure is pleased by the answers and reveals themself. It's a woman with a glimmering crown and hair that glows like dew. Luigi and Chainling recognize her immediately as Empress Aqueena, the sovereign of the Bubble Dew Empire. When asked why she's here, she says that there's a reason for the monster's attacks - Alcoberta's orders - and she holds info about Luigi's keys. They are, in fact, called Rend Keys, items built to teleport between dimensions, each with designated locations for their bearers to travel to, confirming what the professor presumed. She also adds that if they are close to the other half of the broken key, it'll emit a rainbow flash.
Meanwhile, Alcoberta is witnessing the conversation from the tallest hill, finding out that Aqueena is in Wasab Valley. He leaves Hol-e with the monster, ordering them to surprise Luigi's group when they arrive. Aqueena goes on ahead while Luigi, Sonic and Chainling catch up to her. Finally, they reach the top of the highest hill, where Hol-e awaits. Aqueena totally outmatches her, but the flower demon releases a shower of exploding petals, giving the monster it's que. It raises it's enormous body out of the ground, revealing itself to be a dragon-like creature. Hol-e declares it lunch time, referring to the beast as Dralegon. Luigi, Sonic and Chainling head to a cave while Aqueena does her best to hold off Dralegon. Inside, they discover a giant, metallic mushroom. Figuring they can use it to beat the draconic monster, Sonic and Chainling beat and grind it up until it's good to eat. Luigi reluctantly absorbs the mushroom, winding up the same size as his reptilian opponent, now with a robotic superhero look. Sonic and Chainling jump onto his cap and prepare for the mighty clash of titans, with Aqueena showing how to use souped up giant attacks.
Ultra Iron Luigi conquers his foe and knocks him out. With his new form no longer needed, Luigi changes back to normal. Upon inspection of Dralegon's body, Aqueena finds that there's something damaging him from the inside, causing the big lizard massive pain and making him mindlessly destroy things under the villains' orders. Despite their hesistance, Mochiwinkle flies Luigi, Sonic and Chainling into the belly of the dragon, hoping they can find the source of his suffering.
Inside Dralegon, the three adventurers fight off a horde of Chompagne enemies and come across something disturbing. The people of Wasab Valley that have been eaten are to be assimilated in it's stomach and reconstructed into the very same seeds that were being molded into Chompagne monsters back at Shiitak Mines. However, there's more to it. There's a spiky, meatball-shaped abomination licking the seeds and morphing them into fanged creatures made of a corrosive liquid. Thankfully, there's still many people of the valley alive, but they're unable to do anything about their future fates. Luigi and company, however, are not going to stand by and watch this, so they press on. They approach the meatball monster, but it runs away, leaving the team to fight the liquid atrocities. Soon, they use Mochiwinkle to fly up to the heart of Dralegon. At the top, before the heart area, the broken Rend Key lets out a rainbow signal. This is where the beast is cornered. Charging at the crew with a loud cry of "THORACK!!!", a fierce showdown is had.
Despite it's efforts, the monster is destroyed by Luigi's crew. Upon it's explosion, the second half of the second Rend Key is revealed and swiftly grabbed by Sonic. Before they can celebrate, Dralegon spits them out, along with all the others he had eaten; they would've been toast right there if Aqueena wasn't around to break their falls. Once all is said and done, they find that the evil-doers' big pet is no longer violent. He's extremely happy that Luigi and friends managed to end his suffering, and wants to show his gratitude. He releases a fragment of something from his nose, giving it to Luigi. Aqueena recognizes it as a piece of the Miraculous Heart, knowing so as she owns a piece of it herself. It looks like Dralegon gave up his piece as a way to repay Luigi's team for their heroic, life-risking deed. Sonic shows the Rend Key piece and asks Luigi to get out the other. The pieces connect perfectly, making a complete Rend Key for them to use. Hol-e appears to congratulate everyone on their efforts, but warns them that no victory is worth getting cocky about, for pride comes before the fall. She thens disappears in a cluster of flowers.
The people of the valley realize that they're in the presence of Empress Aqueena and freak out joyfully. She calms them all down with her Wave of Peace, remembering why she doesn't like to attract so much attention. Turning the new Rend Key around, Luigi opens a new portal back to Mobius Black. Sonic, feeling patronized, thinks about setting out on his own to look for Alcoberta. However, they decide the next best move is to see the professor again.
Back at Rabbabite Burg, they talk with M. Pestle, with Aqueena back in her trenchcoat and Chainling geeking out over the great scientist. He determines that the fragment is able to sense the aura of dark hearts, like those of the Chompagne Clan. Whenever they're in a place where they can find Chompagne members, the fragment will let them know. For their trouble, he gives Chainling some equipment, and the whole party some communicators called Lunar-Talkars. Noticing that Mochiwinkle has taken some abuse, the good old rabbit upgrades his sprite-like creation with a stronger set of wings, more powerful limbs and a compartment for carrying the fragment. Suddenly, Rabbabite Burg is under attack again. Luigi, Sonic, Chainling, Aqueena, Mochiwinkle and M. Pestle go outside to see what's happening. Alcoberta has shown himself, holding C. Pestle and Sagi captive in energy cages. Sonic, happy to have a shot at Alcoberta again, attacks. Hol-e defends her master, sending Sonic flying back while commenting that in a large class, alas, there just has to be a student where words of wisdom go in one ear of theirs and out the other.
Luigi, Sonic, Chainling and Mochiwinkle agree to use the newly fixed Rend Key to escape back to Mobius Black. Aqueena calls out to the departing good guys to look out for one called Volkingno. Alcoberta spits out a flurry of explosive saliva balls around the town, knocking out every single citizen, including the professor (who goes flying back into his house and painfully crashes down to his basement), before taking off in the airship with many of the unconcious townspeople captured in bubbles. The disguised Aqueena flees.
Meanwhile, on another part of the Rice Archipelago, Amy, Peach, Zipop, Cream, Captain Toad and Toadette are travelling through dark woods, unsure of where to go. They go through a maze, trying to find the light that'll lead them out. Before too long, they wind up in a large, open area where to their surprise, the Koopa Troop is operating. The one's who stand before them are the top minions of Bowser: Bowser Jr., Kamek, Boom Boom and Pom Pom. They're working on a new mechanism for Bowser and a new associate of his. When Peach asks about new partner, the four villains have no reply, but instead, a call for their squadron. Koopa Troop followers and Badniks appear. Amy and Zipop volunteer to take them down, with positive results. The mechanism is brought up to the sky with hidden rockets. Zipop opens up a dimensional portal so he and Amy can give chase.
Up in the air, the mechanism latches on to the bottom of Alcoberta's airship, and a hidden door opens for Bowser's elite minions. Amy and Zipop, now in the engine room of the ship, decide to sneak around and find out about Alcoberta's next move. They get to a data room, but duck for cover when they find out that Bowser and his new partner, a creepy figure covered in darkness with robotic motions, have already managed to discover a computer with information on what Alcoberta is about to do.
According to what they've found, sucking all the joy, love and virtue out of the worlds of Toadstool Earth and Mobius Black is only the beginning. The goblin-bat demon has plans for mutation and spreading evil. What's more is that the species of Alcoberta and Hol-e are revealed on that very same computer. The former is said to be a member of an otherworldly, diminishing race called the Goblats, while the latter is a member of flower-based people called the Brewssoms. Then the shadow figure talks about the mechanism the elite minions were working on. When the device is perfected, he'll use it to hijack the operation and use the mad Goblat's devices for his own ends, like building a world where a mechanical empire conquers all. Bowser expresses one simple desire: to knock Alcoberta down a hundred pegs. To the shock of everyone, Alcoberta and Hol-e arrive in the room with their Chompagne soldiers. Amy and Zipop get freaked out, giving their position away. Bowser Jr. points them out as the "Snooping Toms" who bothered them just moments earlier.
Bowser is not pleased by how a little girl and a guy in a crime-fighting uniform have given his top underlings grief. Kamek vows to make up for past mistakes by having him and the other elites take the hedgehog girl and strange detective as a complete unit. Alcoberta sneers at Zipop, disclosing that the Lightning Streak of Justice is a "Sobad", a good-for-nothing goody-goody who acts all high and mighty until they have to make a decision that could either break their reputation or dwindle their spirit. Alcoberta presents C. Pestle and Sagi, threatening to drink their life juices. Zipop demands they be let go. Alcoberta quickly releases Sagi, saying he's no monster, and he likes to trade. In exchange for Sagi's safety, Alcoberta forces Zipop to surrender his dimensional portal opening powers, effectively crippling him. Instead, Zipop now has to open portals with a limited supply of tokens, and even then, the portals are weaker than before. Bowser, the Koopa Troop elites and the shadow figure disappear from the scene in a cloud of fire.
After a while, the airship, which everyone finds out is called the Goblampire following an annoucement of the attached cannon's preparation, locks on to the Rice Archipelago. The cannon charges up and emits a cloud made of rainbows, before blasting out that enormous laser that annhilated Peach's Castle, part of Toad Town and the area around Mt. Oak Nut. The laser splits the Archipelago in half, separating Rabbabite Burg from Wasab Valley, both parts drifting off to sea. Amy, Zipop and Sagi are trapped in bubbles, forced to watch part of the world they see break apart. Back on the ground, Peach tries to keep everyone calm while Cream, Captain Toad and Toadette panic. They make it to the coast, where they see that the island is moving away from the Mushroom Kingdom. Right then and there, Aqueena, still in her trenchcoat and now riding a sailing jellyfish, tells them all to get on. They do so and enjoy a ride back to Toad Town.
At that moment, the Goblampire makes a dimensional jump back to Mobius Black, where Luigi's party is headed. Hol-e tells Amy, Zipop and Sagi that there's no cowardice in backing out of a fight they can't win, saying that what they're going through now is the consequence of perserverance driven by stupidity. Alcoberta has them taken through two dimensional portals (Amy into one, Zipop and Sagi into the other) made with his own hands, making no specifications of where they're going to end up. Afterwards, the nasty hybrid orders his subordinates and right hand girl to seek out "the turtle-ox and his weird colleague" before they become a problem.
Back with Luigi, Sonic and Chainling, they arrive in a town where Verity is waiting for them. Accompanied by some of the animals in the town, she discloses the name of the place, Sunset Heights. Verity tells everyone that she concluded her service to Shoguffaw and was allowed to roam freely around this civilized area. Luigi, having overheard the last words shouted to him by Aqueena, talks about the one known as Volkingno, and how that character may be essential to the quest.
One of the townsfolk, Meowiko, tells about a legend surrounding this Volkingno person. He's said to be a heavy sleeper, but a powerful giver or destroyer of life, depending on his mood. Rumors also say he holds a sparkling fragment of something that makes miracles come true. Luigi takes out the fragment he's holding, and Meowiko instantly asks where he got it. When Luigi answers "a gigantic dragon controlled by this flower girl", the cat girl is in disbelief. She knows well that there couldn't be more than 4 bearers of these magical fragments. Sonic says that Aqueena called it a piece of the Miraculous Heart, not really knowing what such an artifact is. Meowiko then begins to wonder if Volkingno is another Miraculous Heart fragment bearer, and if the one in Luigi's possession is a fragment belonging to a bearer that nobody can remember. Verity decides that Luigi's team should head towards the north to Demise Wastes, hoping they can reach the domain of Volkingno from there, predicting he might live in some exceptionally hot place. Verity shows the way to the horrid desert before eagerly rushing ahead.
Upon entering the wastes, Sonic starts feeling uneasy. He tells Luigi and Chainling to mind their own business and get going when they simply ask about it. They fight against deadly enemies on their way through the wastes, reaching a temple at the edge. Sonic starts having flashbacks to somebody he remembers as the team steps toward the entrance of the temple. Inside, they run into a spectre that asks them about their greatest desires. Luigi says "my brother", Chainling says "the safety of my home on the Rice Archipelago", but Sonic says nothing. The three of them are locked down on the floor, and the walls start to close in on them as poisonous, scorpion-like monsters emerge from the floor. Luigi pleads Sonic to open up. When the situation gets to a critical point of hopelessness, Sonic finally says "to honor her memory!".
He explains that he once protected Mobius Black from the forces of the villainous Dr. Eggman with his most trusted, faithful, equal companion - a chipmunk girl with red hair and blue blades of energy - never stopping until the battle was won. He says she was the daughter of a royal family. When Sonic grew feelings for this girl, he dedicated his life to serving her and the family she held dear. They married and became the new lord and lady of Mobius Black. But then, friction rose in the relationship when Sonic felt inept at ruling the worldwide kingdom. The girl didn't know what to do with her groom, and left to find a way to make him a better king. Sonic remembers her going to the Demise Wastes and never returning. Ever since her apparent departure, Sonic has been trying to make a better king of himself, but alas, nobody really seems to care for his sovereignity, except for those who have stuck closest to him in the battles of the old days, such as Tails, Knuckles and Blaze. The name of Sonic's bride has never been spoken since then, for the mention of the royal woman only brings back painful memories.
Luigi and Chainling have their jaws wide open from this discovery, and just then, they're all let go and allowed to move on with their quest. They go into the next room and find Verity, standing by a large totem pole. The spectre from before enters the totem pole, revealing it as it's body. It calls itself the Destructotem. It says that Verity got past the previous room saying she wanted "to get at a wicked sorcerer and his venomous minion". Three smaller totem poles rise from the ground, with different signs on them. Luigi, Sonic and Chainling are instructed to approach specific totem poles out of three, telling them to take these magical powers. Verity tells them what they have to do by revealing she has a magical power that involves summoning a ball of Ice and making it burst. Luigi, Sonic and Chainling put their hands on their respective totem poles and learn how to use magic. Luigi makes Lightning, Sonic makes Wind and Chainling makes Water. Just then, the four of them sink into the floor.
The green man, blue hedgehog, agile Chain Chomp and vigorous woman fall into a dungeon area, where there is no light. Using his newly acquired Lightning Magic, Luigi lights their way through the dank caves of the temple. In another area, Sonic has to use his Wind Magic to create tornados that'll bring everyone up to another level. After that, Chainling uses his Water Magic to douse enormous fires in a big puzzle. In the last room, Verity uses her Ice Magic to create a bridge to the other side of a giant gap. Soon, they reach a room full of tombs. Destructotem appears, telling them all that they have done some clever thinking to escape the dungeon. But then, he dubs them "vandals", for wrecking the air conditioning and ruining the heaters for the master bathing pool. He summons an army of the undead, hoping to take them down, but the army is beaten without the team breaking so much of a sweat. Suddenly, a tail comes out of the ground and snatches Verity, dragging her down to another place.
The temple is searched, with many walls and ceilings being broken in the process until Verity is found in an area that looks like a gigantic bed made of sand. Destructotem orders the owner of the tail to crush the "vandals" with all it's might, calling it "Rancorpion". Rancorpion emerges from the sand with Verity in it's clutches and attacks Luigi's crew. After a mighty fight, the heroic trio destroys the monstrous, scorpion beast, freeing Verity and surprisingly, a new cut-in-half Rend Key. Sonic is unimpressed by the reward for all their hard work, but Luigi checks for a signal light. It appears to point east. Verity says they gotta leave this dreadful place at once, just as Destructotem orders an army to come after the "vandals", who make their escape through a nearby quicksand pit. At the bottom, they fall into a room with a small platform and a floor covered by spikes. Chainling uses his chain to swing the crew around to an open window. This is where they finally get out of the temple.
The undead army comes after them, prompting Sonic to grab his teammates and run as fast as he can with them. Little do they know at that moment, some robotic figures, who call themselves the "Hard-Boiled Heavies" are watching their every move, planning to strike with the element of surprise.
Soon, the entire party is out of the desert and standing on a pleasant path full of checkered dirt. Verity, realizing she has forgotten her manners, says "thank you" to Luigi and company for saving her from the temple's monster. She gives Luigi a kiss on the cheek, making his face glow red. Chainling suggests checking up on Professor M. Pestle, but the others aren't so sure if they can reach him from a different world. Chainling tries activating the Lunar-Talkar anyway, and it works, to everyone's amazement. As they get M. Pestle up to speed on current events, the good Rabbabite scientist informs everybody that the Rice Archipelago has been split apart, causing so much damage to nature and technology in the process. He also tells them that not only does Alcoberta have his son and grandson, but everybody else in Rabbabite Burg besides himself.
Thankfully, the villains thought the professor was terminated. There doesn't seem to be any sign of Alcoberta left on Toadstool Earth, meaning he's on Mobius Black again. Sonic considers abandoning the Rend Key quest to hunt down Alcoberta, but when asked if his wife would want him chasing after a fight he can't win yet, he decides against his rash idea. Verity says hello to the professor, and he asks if he's joining the team. She says that she'll be tagging along with Luigi and friends from that point onward, since C. Pestle is her friend, and she doesn't want to meander around while a horrible monster is doing atrocious things to him. With that, she has some equipment and her own Lunar-Talker transferred to the crew's current location. Agreeing to continue looking for Rend Keys, Luigi points where the Rend Key half is pointing now: northeast.
Suddenly, from the direction of Demise Wastes, from where they came, a shadowy creature made of mist appears. Sonic recognizes the shape of the creature, believing it to be the girl he talked about. It silently flies toward the area northeast from where the crew is standing. Uncertain of what that was about, they follow the creature and the Rend Key half's signal light. With a team of four, Luigi has gained hope that Mario will be much easier to save now.
To be continued...
As stated above, the game takes after the Mario & Luigi video games. The battle system gives each character three basic attacks: the Jump attack, the Weapon attack and the Magic attack. Depending on the timing of button presses or how much a certain other requirement is fulfilled, the performance of an attack can be rated "Poor", "OK", "Good!", "Great!!" or "Excellent!!!". On the enemies' turn, the chance to dodge and/or counter is given, whether it's with Jumping, a Weapon or Magic. Both allies and enemies have Health Points, and whenever their Health Points hit '0', it results in a K.O., removing them from the battle. However, there are notable differences this time around, including the recruitment of multiple party members throughout the adventure, character-specific moves learned by leveling up, having up to four playable characters in combat at once, and the new Heat-o-Battle meter; a gauge of building intensity that applies to both the players and the A.I.-controlled enemies. It can be beneficial or harmful, depending on how far it escalates. A fully loaded Heat-o-Battle meter can allow a single character to perform Overheat Attacks; incredible moves that do damage to the user to inflict an insane amount of damage to the opponent(s).
Over the course of the adventure, Combo Attacks can be acquired by picking up 5-10 Battle Pieces for most, while others are obtained through particular events in the storyline. They come in three varieties: Duo, Trio and Tetrad. These cost Battle Points (BP) to use, and each one requires a specific combination of player characters on the battlefield.
Toadstool Earth and Mobius Black serve as the main overworlds of the game. Luigi and his party members - two characters at a time - can explore non-linear landscapes and linear dungeons to jump across platforms, find items or coins in blocks, hit blockades and switches with a hammer or some other strong weapon, activate mechanisms with magic moves and engage enemies in battle by touching them, hitting them first, or getting struck by their own attacks. As the game progresses, Luigi's party can learn Combo Actions; special moves that can help get to areas that seem impossible to reach at first, or solve puzzles.
In some portions of the game, Luigi will face giant bosses which he will need to grow into a giant himself to face. By finding a conveniently placed Ultra Iron Mushroom in the area, he can become the enormous Ultra Iron Luigi (with the look of a robotic superhero) and do battle with his colossal opponents. Like in normal battles, he can fight the enemies and dodge/counter their attacks using his Jump, his Hammer and (from the second giant battle onwards) his Lightning. He can also use Giant Combos to replenish his health, strike hard with a spinning Jump attack, deliver a furious series of Hammer swings or unleash a powerful Lightning bolt. However, he must use these wisely, because after every Giant Combo, the partners will become exhausted, disabling these useful moves for the next three turns. When the giant boss' health reaches a critical point, Luigi can end the battle with a Finishing Combo. To perform this move, he jumps into a storm cloud high up in the air, and charges his right fist into a big energy glove, with his partners activating a field of electricity around Luigi by tapping the big, metallic 'L' on his cap. He then flies down into the boss with a mighty punch, while the rest of the team rides on his back as if it were a surfboard. If he hits the target marker on the boss, he'll get an "Excellent!!!" K.O., winning more coins, items and helpful gear. If he misses the target marker, it'll just be a "Good!" K.O., with a smaller reward in coins, items and gear.
The game's main story has three save files. The player's progress can be saved anytime from the Pause menu outside of battles and cutscenes.
A notable feature is an in-game bestiary that records every new enemy encountered, complete with detailed descriptions.
The younger, yet taller, underdog brother of Toadstool Earth's champion, Mario. When his homeworld is under attack, he goes through what may be the darkest time of his life. The experience may leave him more resolute than ever before to set things right.
Once a compassionate, charming, charismatic hero who obeyed only the wind, he has now become a surly despot. Clearly, there are some grim details regarding his unplesant change. Despite that, he'll form necessary alliances against those who dare to threaten Mobius Black.
A fast moving, sharp-witted superhero from the Cidimension, known as the Lightning Streak of Justice. His mission is to prevent disaster across the multiverse when the deadliest, most terrifying villains from his homeworld threaten to destroy and conquer all there is.
A beautiful, sassy investigator who grew up in the Rice Archipelago. She's on a quest to discover the truth about the threat from the Cidimension, armed with a mace and ice magic. She's eager to help out a hero in need, winning the affection of a certain virtuous soul.
A friendly Chain Chomp from the Rice Archipelago who has learned to live a peaceful life with other creatures known to be enemies of the Mario Bros. in the past. He has learned how to use his chain as a powerful tool for support and defense. Rolling is his favourite pastime.
A talkative, robotic sprite created by the inventive supergenius, Professor M. Pestle. Despite it's small size, there's plenty of functions that this flying friend can serve. In the heat of battle, it'll lend a hand in avoiding the deadliest attacks.
Professor M. Pestle:
The revered, technological, rabbit-like inventor of the Rice Archipelago. He's responsible for some of the most advanced machinery on Toadstool Earth. On this long journey to stop a couple of criminals from another world, he's going to provide only the best tools for the job.
The reality warping, dimension travelling megalomaniac hailing from the Cidimension. He's bound to siphon the joy, love and virtue from the worlds of Toadstool Earth and Mobius Black after being freed from a high security prison. There's no equal to his magical prowess or lunacy.
The little girl who loyally serves Alcoberta. While her partner is insane and cold, she, herself, is balanced and jovial. It's unwise to be dazzled by her cute looks; she holds a bottomless pit of poison literally at her fingertips, and that giant flower on her back is no mere decoration.
Alcoberta and Hol-e's servile followers. They come in many shapes, sizes and colours. Some may even look like enemies that Toadstool Earth and Mobius Black have faced before.
Luigi's older brother, and local hero of Toadstool Earth. Despite his legendary status, he was unfortunate enough to be captured by the invaders from the Cidimension. He has more faith in his younger brother than anyone else does.
A pink hedgehog from Mobius Black who used to be madly in love with Sonic. She's not very fond of what the blue hedgehog has become as a result of a dire event. She fights enemies with her heavy boots and her trademark Piko Piko Hammer.
The beloved ruler of the Mushroom Kingdom, known for her kindness, class, beauty and unfortunate tendency to get kidnapped. She's been a close friend of Luigi for a long time, helping him whenever she can. This time, she'll play her part in the rescuing of Mario.
The sovereign of the Bubble Dew Empire, she has ruled over the Sea Maiden people with discipline and intelligence. She possesses control over all forms of liquid, but always respects the pride of good-natured citizens. In her possession is a fragment of an all-powerful artifact.
Commander Tails, General Knuckles and Chief Blaze:
Sonic's elite guard. Tails supplies the brains of the bunch, Knuckles lends his indominable strength, and Blaze combines speed with her pyrokinetic powers.
The Mario Brothers' long-time arch-nemesis and the most persistent villain on Toadstool Earth. He was on the way to instigating another princess kidnapping plot with his Koopa Troop, when he was beaten to the punch by the Cidimension's deadly forces.
The old arch-enemy of Sonic and the most notorious tyrant on Mobius Black. Long ago, he conquered the world and declared war with his robot army. Thanks to the efforts of the blue hedgehog and his allies, the planet is free and the doctor is history. Or so they think...
- Sonic the Hedgehog's portrayal in this game was inspired by less friendly, more irritable depictions of the character from outside the Sonic video games.
- Originally, Wario and Waluigi were going to be the main protagonists. At a later stage, it was decided to only have Wario, with a cap wearing Goomba named "Goomboy" replacing Waluigi. Following the Year of Luigi, the game was overhauled to have Luigi as a key character. Finally, Wario was axed from the starring role (and the entire game) in favor of Luigi, and Sonic became the deuteragonist.
- Alcoberta was originally named Kackleberto, and later Krackleberto. These names were scrapped because of sounding too similar to the first main villain of the Mario and Luigi series, Cackletta. Additionally, Hol-e's initial name was Strongo. The names Alcoberta and Hol-e were ultimately chosen with a naming theme in mind.
- Sonic's bride is mentioned numerous times throughout the game, but is never shown in full or referred to by name. However, she's heavily implied to be Sally Acorn.
- Despite being near silent in the Mario & Luigi games, Luigi himself has full, visible lines of dialogue in this installment.
- Many of the game's events are like those seen in the Mario & Luigi games.
- This game has been in development since the mid-2000s.
- Elements from Sonic Mania, Sonic Forces and Super Mario Odyssey, were thrown in late in development for promotional purposes.