Toadsworth leads Mario and crew to Grassland Hills for kart practice, where evil awaits... It's Bowser! Bowser brought his baddies to make sure Mario and friends don't get the nitrolizer! But, Lakitu fights back for the nitrolizer and they keep fighting until Dimentio steals it! Bowser gets angry and joins forces with Mario and crew. Then you pick your character. You race all 8 courses until after Spinning Mountain,where Dimentio comes back and uses the nitrolizer's power against them. Queen Bee gets angry at Dimentio, and challenges him to a one on one race. Then you play as Queen Bee in a race against Dimentio on Spinning Mountain. Then Dimentio is enraged of losing and takes Queen Bee to Dimention Mirror. Then, you use your character to save Queen Bee. After that, Dimentio reveals he has more minions! Dimentio sends Fawful to punish them at BeanBean Kingdom. Your character challenges Fawful andafter winning Fawful runs away, crying. Rosalina sends lumas to catch Fawful, and they do. Fawful is held prisoner at Rosalina's Observatory, but throws a potion which causes Rosalina to get angry at your character. Rosalina challenges your character to a race, and you accept. After winning, you get Rosalina back to normal. Bowser says to  go to his castle to rest. you do, and bowser says he smells Dimentio. Dimentio comes and challenges Bowser to a race. You play as Bowser in a race against Dimentio. Bowser wins and Dimentio flees.Wiggler takes the party to Goomba Woods where it's safe. You go and play a race. Suddenly, E.Gadd pops out and tells you to go to Paper Theater and Rainbow Road, where there are parts  to make another nitrolizer. After going to Paper Theater, Bowser Jr. ambushes you and challenges you to a race. After winning, you scare away Bowser Jr. and go to Rainbow Road. You make another nitrolizer and challenge Dimentio. You win, and Dimentio begs for mercy. All the bad guys join you and you've completed Story Mode.

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