Ninjis are enemies that first appeared in the game Yume Kōjō: Doki Doki Panic and its Western remake Super Mario Bros. 2. In the game, they either hopped up and down in one spot, trying to attack the player, or ran back and forth, jumping when near. The player can simply defeat it by jumping on it's head, then picking it up and throwing it at an item or another enemy. They made a very minor appearance in Super Mario World where two could be found in the last room in Bowser's Castle. Like their previous appearance, they too bounced in place, in a total of three times with each additional jump being slightly higher than the first, and could easily be defeated like normal enemies by use of jumping on them, fireballs, Yoshi, Starman, Cape, or Mario could simply ignore them. There is only a purple variety of Ninjis in this game.
In Paper Mario, rather than an enemy, they were a race of peaceful characters and were the protectors of the star kids at Starborn Valley.
Ninjis only appeared in Karate Koopa. They captured Princess Peach. Mario, Luigi and Masaki battle the Ninjis to defeat them and rescue Peach. They have Japanese accents. They were called "Ninjas". They are Koopa's minions.
Ninjis only appeared in The Yoshi Shuffle. They are brown instead of black and they appear without a single tooth.