CatBat is the boss of the Sapphire Passage in Wario Land 4 that resembles a grotesque, ghostly cat creature with a bat's head on top of it and ears resembling the bat's wings. CatBat floats around a water-filled room with platforms for Wario to move on and a harmful drill device in the water that will attack him if he falls in.

The room periodically summons large tidal waves, which Wario uses to attack the beast by jumping on them and then charging at the bat on top, which is its weak point. When damaged, CatBat will spew three one-eyed spiky little monsters from its gaping maw to attack Wario with. At first, they cause him to turn puffy, but after a certain point the spike creatures will become red and actually damage Wario.

After taking a significant amount of damage, the bat head dies and Wario has to deplete the rest of the boss's health by pounding onto the cat creature's exposed head. The waves which are used to attack it also start bobbing up and down, making it harder to jump onto the boss correctly.