Clean Kat/Sinister Sludge is Captain Good's/Phantom Phink's pet cat/dog. Clean Kat is a white and snobbish cat while Sinister Sludge is a sleazy brown dog who's usually told by Phink to shut up. Whenever Good/Phink morphs, Kat/Sludge morphs at the same time (although he is capable of doing it separately from his master, such as in the Saturn 500, when Phink says dogs aren't allowed on Mars and he morphs, causing Phink to say cats aren't allowed, either, and in the Mizar Marathon when Good said that cats aren't allowed in a castle, to which he morphs and Good says that goes for dogs, too).