He is much evilver than Dr.Eggman could be and he was even more power hungry which led to his alliance with Marceline's Dad because the blue demon lord liked the challenge of controlling psychopaths like The Joker so he took Nega to be a member of his team, after diposing of Inferno Scorpion's powers and dropping him off after he got so unnerved with the clown. Eggman Nega used his likeness of Eggman to his advantage by using as soon as the V Team arrived. He meet experiments in his lab and an area which Marceline's Dad told him to stack with weapons knowing they would use them anyway and he was right when Negaduck used on the clones and after Scrouge killed Eggman Nega
During the sequel, Eggman Nega during the first adventure is recruited by Eobard to join his past villain syndicate alongside a lot of Hunson's more uncontrollable allies. He works once again with his old allies Darkwarrior and The Joker the latter who he listens alongside Thawne to.
He joins The Joker with many of his assocaites and leads an attack on his former boss while The Joker makes his other plan going well. Eggman Nega and Tarus both owning the file that The Joker and Mike obtained for Darkwarrior give to him on Sektor's Orders