ThunderCats (1985) : 2x9

The Madd Bubbler, an ancient creature of third earth who lives in an old Thundrilium mine on hook mountain has the power to turn all creatures into evil beings, and making people accept his modo - "destroy, or be destroyed". He manages to seduce the Luna-tacs to fight against each other, and afterwards Panthro, Tygra, and Cheetarah. They fall under the bubblers power and begin fighting each other to the death. Lion-O, observing these occurrences through the sword of omens finds out from Jaga that snarfs are not capable of evil. He summons Snarf and Snarfer and tell them to retrieve the Thundercats from the mine so that they can be returned to their normal selves.