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Mellow Kitty is an enemy found in Wario: Master of Disguise. It is found in Carpaccio's Lab, and only one of them appears in the game. It appears to be a cat-like bubble with a teal design surrounding it. It attacks by consuming Wario. Any non-physical attack defeats it, and being tapped by the stylus several times after eating Wario works too. The name "Mellow Kitty" is a pun on Hello Kitty.
While inside a Mellow Kitty, Wario loses experience points for his currently-selected disguise, but he does not lose any health. He does not, however, drop a level. Therefore, once Wario has leveled all his disguises up to Level 3, this enemy is harmless.
This cat burglar has no interest in the true value of his loot. He just likes to stare at shiny things.