Queen Ruby, better known as simply Ruby, is the ruler of the Underworld and serves as a major character in Super Mario and the Underworld Trials. In the game, she helps Mario and co. escape the Underworld by telling them that the Mystic Stones must be collected by complete the Underworld Trials in order to escape.
Ruby resembles a tall, middle-age woman with light-gray skin. She has red hair and, like the other Underworlders, is crystalized. She also has pale blue eyes and a mouth.
Ruby's attire consists of a pale red dress with blue and white accents, and several blue and pink jewels around the torso. This dress is cut off on her left side, revealing that under this dress she wears a dark-red leotard and yellow high heels. She also wears blue diamond-shaped earings and wears a yellow crown with a blue gem in its center. She also wields a yellow trident and wears white arm-length gloves.
In Super Mario Kart: Switch Circuit, when using a bike or ATV body, Ruby will instead wear a dark red biker suit comparable to that of Peach or Daisy. Unlike the other bike outfits, which are white with different-colored outlines, Ruby's is reverse; dark red with white outlines.
Though the ruler of the Underworld, Ruby is kind and benevolent, preferring to do what will benefit everyone rather than do what will benefit just herself. She also often puts others before herself, willing to sacrifice herself for someone she loves. Ruby is also generous and caring, allowing Mario and friends to stay at her home while they are in the Underworld. She is also quite wise, having a great knowledge of the Underworld.
Another side of Ruby is her motherly personality, mostly seen when with her daughter Pearl. She is always willing to help her daughter with anything, as well as play with her when she's happy or make her feel better when she's sad.
Ruby's abilities are channeled through her trident. Using it, she can perform a wide variety of magic abilities, ranging from simple tactics like telekinesis to creating portals. She has also been shown to use offensive tactics, such as materializing crystals and using them against her opponent, but only uses them when the situation calls for it.
Among her other abilities are having above-average cooking abilities. In particular, Pearl describes Ruby's strawberry shortcake as "the best she ever tasted".
Ruby makes her fist appearance in Super Mario and the Underworld Trials. When Mario and co. fall into a pit leading to the Underworld, she is the one to explain that in order to go back to the Mushroom Kingdom, the Mystic Stones must be collected from the Underworld Trials. During their stay, Ruby lets Mario and friends stay in Pearl's room, much to her daughter's delight. Throughout the game, she gives advice to Mario and, along with Pearl, cheers him on.
At the end of the game, Ruby's younger, evil sister Obsidia makes her presence, and uses the portal to the Mushroom Kingdom, taking Pearl with her. Ruby then reveals that she and Obsidia used to rule the Underworld together, but once she saw her plans of universal domination she trapped her in a crystal. She uses her powers to create a temporary portal to the Mushroom Kingdom, allowing Mario and the others to stop Obsidia and rescue Pearl. After the final battle, it is revealed that Pearl is actually Obsidia's child; Ruby found her as an infant after her sister's imprisonment, and decided to raise her as her own. Pearl says through tears that she wants Ruby to be her real mother. Later, she takes a group photo with the rest of the characters and the game ends.
Ruby makes her first playable appearance in Super Mario Kart: Switch Circuit as an unlockable playable character. In this game, she is in the cruiser weight class, having high speed and weight but low handling and acceleration as a result. Under normal circumstances, she must be unlocked by obtaining a three-star rank on all cups in the 100cc engine class, including the 8 Cup. However, if one has a save file of Super Mario and the Underworld Trials on their Nintendo Switch, she alongside Pearl, Belle, Brooke, Brittany, and Sarina become default characters. Like the aforementioned characters, Ruby's special item is the Mystic Stone.
Ruby makes her second appearance as a playable character in Mario Kart: Speedway Rush!, being a cruiser character once again. As with Super Mario Kart: Switch Circuit, she is automatically unlocked if one has a save file of Super Mario and the Underworld Trials on their Nintendo Switch. Otherwise, she can be unlocked by playing 2000 races total. Her partner is Pearl.
Ruby reappears in the expansion for Super Mario and the Underworld Trials, The Rescue Squad: Birthday Blitz. She plays a slightly more minor role in this game. She summons the Rescue Squad to the Underworld to get them to help set up Pearl's upcoming birthday party by inviting the royal families if the neighboring Kingdoms. Throughout the game, she is seen giving encouragement to the Rescue Squad, though is slightly more secretive of her intents whenever Pearl is around.
Though Ruby doesn't physically appear in Sleepover Adventures, she does make a cameo, making a phone call to L.K., Timid Guy, and Trumbone to send Pearl and her friends to bed. In the game, it is stated that she is on a royal trip to another kingdom.
Ruby appears as a playable character in Super Mario Spikers, appearing as a Balanced-type Captain. Her outfit consists of a light-red outfit with arm-long sleeves, with a matching miniskirt. Her wrists and legs also have crystals jutting out of them, which are identical to her hair. Furthermore, thanks to a new spell she learned, she also has wings constructed out of special crystals, which she uses to fly around. Her emblem is her trident, and her theme is Trip Hop.
Ruby doesn't physically appear in Super Mario Expedition, but she is briefly mentioned by L.K., Timid Guy, and Trumbone at the end of the game, taking Sapphire by surprise. When they leave, Platinum asks why he was so curious about her, to which he reveals that she is his sister.
Ruby appears in Mario Kart: V² Circuit as an unlockable character. Like the rest of the characters, she can be unlocked randomly by placing first in a Grand Prix on any engine class. Alternatively, she can be purchased at the shop by collecting Coins. She has average speed and acceleration, above average handling, and average traction. She is a heavyweight character, albeit on the lighter end of that spectrum.