King Boo is the king of all Boos, and although he is not the biggest Boo, he is the most powerful of his kind. The only staff time trials course dedicated to him is SNES Ghost Valley 2 (Mario Kart Wii). He is very sneaky and can summon anyone's special item in Mario Kart: Double Dash!!. He is an unlockable character in Mario Kart: Double Dash!! and Mario Kart Wii. In Mario Kart DS, he is a boss in Mission Mode, and like all bosses he came from Super Mario 64 DS, but was mistakenly called Big Boo in Super Mario 64 DS.
Despite being an excellent handler, King Boo is a mid-tier character for his poor raising stats. King Boo is often used for courses with tight turns, such as Rainbow Road. Although in the mid-tier placing, King Boo has great rivalries with other characters and has excellent racing skills, making him a character with high-tier or highly possible, top-tier character categories since his handling stat raises any kart or bike, including the Spear.
- Standard Kart L
- Flame Flyer
- Piranha Prowler
- Wario Bike
- Standard Bike L
- Flame Runner
- Shooting Star
Staff Ghost Tracks
- Interestingly, King Boo is one of the heavyweight characters, despite being a floating, weightless ghost. This may mean that his crown weighs a lot or because of his large size.
- Despite being a "weightless" heavyweight, King Boo is actually heavier than Wario and Waluigi, the same weight as Rosalina and slightly heavier than Dry Bowser.
- King Boo is the only character in Mario Kart: Double Dash!! to not yell when being shot from the cannon in DK Mountain (though in Mario Kart Wii, he does).
- It is unclear why Nintendo put King Boo in Mario Kart Wii since he unable to drive any car in the game due to having no legs.
- Though he owns no track in Mario Kart: Double Dash!!, he is portayed in the Luigi's Mansion Battle Stage's logo; implying that he has some relation to the stage.