In Mario Kart World, 24 playable characters have alternate costumes unlocked by eating food items.
These costumes are part of the game's broader character-unlock system. During races, drivers can collect food items, which unlock different outfits for selected characters. The costume system gives familiar racers additional appearances without counting those outfits as separate playable characters.
A common mix-up is confusing the number of costumed characters with the game's total roster. Mario Kart World has 50 playable characters overall, but only 24 of them are described as having alternate unlockable costumes. The two figures therefore measure different things.
The outfits also connect the racing game to Mario Kart World's open-world structure, where players encounter food and other collectibles while driving through the game's environments.