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Robo-Fiend is the archenemy of the fictional superhero "Ultralord" in The Adventures of Jimmy Neutron: Boy Genius. He is constantly mentioned by Sheen, who is unhealthily obsessed with Ultralord. Not much is revealed about the character, and there does not seem to be much noteworthy about him, as he is described as a very generic and one–dimensional villain. Robo-Fiend only interacts with the protagonists in the episode "Ultra Sheen", where Jimmy uses an invention of his to transport Sheen and himself into an Ultralord video game that consists entirely of fighting Robo-Fiend who can be set to a wide range of difficulty levels. To be safe, Jimmy sets the game to the lowest level when they go in, but Carl Wheezer walks into the lab and sees the game, and not realizing the real Jimmy and Sheen are actually inside, sets it to a very high level for his amusement, which makes things very difficult for Jimmy and Sheen. Robo-Fiend is defeated when Carl accidentally puts himself into the game along with another game called "Llama–Palooza" which also brings a stampede of Llamas into it, and Sheen remembers that the character is Lactose–intolerant, so he sprays Robo-Fiend with Llama milk which makes him explode.