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
Eggman Nega joins Joker's team to flush the parasites for their master and attacks the united alliance of The B Team, THe Legends and Slade's team he though is beaten easily by Jorgen
Phineas, Isabella, Julian, Django and Marceline all wake up from the bomb and they are right in front of Bender, Skipper and other past selves of the heroes.Joker has his eyes on them and informs Thawne and Toffee how to best approach them and Thawne has his own approach to have FANG, Darkwarrior and Eggman Nega go after them. FANG, Eggman Nega and Darkwarrior are all hot on their trail and use the campfire they had to follow them. Phineas and Isabella take out the magic cannon ready to shoot something and it turns the three have found the crew and FANG tries to kill the team with Eggman Nega and Darkwarrior Duck firing big guns at them with Past Bender and Django also firing their own beams while Marceline uses her own vampire powers on FANG to keep him from poisoning the other guys. The firing goes on for a bit until The Joker orders the island blown up
Teaming up once again with Darkwarrior and Joker, Eggman Nega tries to destroy Hunson and Alt Doof under Thawne's orders to get the spear of destiny. Eggman Nega doesn't succeed but masquerades as Eggman to trick Slade's team to lead him to a part. He eventually is killed by Slade when Nega reveals himself too early as using the team.