Most of Mario Kart World’s remaining playable characters also appear as obstacles on the tracks. This design makes the game's expanded roster part of the world itself rather than limiting characters to the selection screen.
The game features 50 playable characters, but only 24 of them are described as having alternate unlockable costumes. Most of the others additionally function as track obstacles while players race.
The idea grew from a sketch of a Cow from Moo Moo Meadows driving a truck. That image encouraged the developers to turn more course inhabitants into non-player drivers and eventually make many of them playable.
These obstacle characters help populate the open world with moving traffic and activity. They are distinct from the player's opponents, who are selected as racers for a particular event.