He is introduced as one of the members of the V Team as Slade and Anti Cosmo call him up to help them in their mission and like the all other villains in the group joins them. But they are defeated as usual.
Slade Strikes Back
He returned again and helped Slade again with his plans but they failed, It had to do with the horror of Joker's returning and every member was afraid of him. So he decided with the others to stop Joker angry at him for his actions
The V Team Island Adventure
This time he was in a protagonistic role with the rest of his team. He played his part and he joined forces with robot rival Bender and other heroes against Uka Uka. with his scientific knowledge he contributed to his victory against him
The Great Time Travel Adventure
Like the rest of the team he returned, And once lend his hand against villains including his future self against Marceline's dad and Darkwarrior Duck who has grand plans to take over.
After the adventure, he helps in the cloning of Ed before Eddy is hauled away on false charges of robbery by Carmelita Fox. Who wonders what he and the rest of the team are doing during Totally Mobian Spies? Dr. Nefarious was helping the V Team take back Mobius during the later parts of the story as part of their deal with the B Team who were keeping their eyes on their leader.
Nefarious joins Eddy, Scrouge and Negaduck in helping the current Slade and Anti Cosmo against Thawne, after The Joker invades their old lair. Nefarious is brought in Hades's chariot to get back to the future Slade's ensemble which is attacked by Alchemy. At his past master's orders he and the other V Team help destory the army. After meeting some of Slade's new alies he and the three don't know, their capture of The Teen Titans is brougt up and that The Joker used his invasion of Slade's base in the past to capture the Teen Titans for his purposes.
When Deathstroke invades their ship, the team ends up splat from each other with Nefarious working with the rest of the team to fight Guzma. They Team up to take on Joker's forces with him going with Eddy, Sideshow Bob and Mojo to get some new team mates, Brother Blood puts them under his control for Mojo to fight himself while Bob gets away with Cold and Lisa.
Eddy wakes up with the other V Team members and stand in front to go after Deathstroke who decides to go after the ship directly now that the heroes know too much. Deathstroke has defeated the 4 which Bob and Anti Cosmo bring back to get them to health.While getting back to good condiiton, Scrouge and Negaduck discuss Deathstroke's frightening efficiency and capablity of fighting as well as skill. Sideshow Bob points out that Deathstroke is after all a mercenerary and assassin. Eddy then adds that he seems to be no nonsense and jumps right into the plot, He even compares Deathstroke as the bigger threat than Thawne which Anti Cosmo disagrees with.
Allies and enemies
Allies: Lawrence, the V Team, Slade, Anti Cosmo, Hades, the Cosmic Empire, Ethan Lectric, the B Team (often)
Enemies: Ratchet, Clank, Joker, Uka Uka, Marceline's dad, the Master, Jack of Blades, M.O.D.A.B (at times), Alt Doof, Taurus Bulba, No Heart, Eggman Nega