"Something like that...but WORSE!" - Negaduck
Negaduck was with the Shadow Force until he made his own team with Ino, Sakura, Miku, and many others. While he was in the Shadow Force, he helped Etna in her plan to win Gabriel back. He didn't play a big part in the Shadow force war. He aided the heroes when Organization XIII attacked. What he's really after and who's side he's on is unknown.
Negaduck soon allied himself with a group of villains, known as the V Team. Though he doesn't see eye to eye with many of them, they are the only friends he has as well The B Team who work with the Team against other threats such as Uka Uka and Hunson Abadeer
Working with Slade and Anti Cosmo
Afterwards he and the V Team were called by Slade and Anti Cosmo to help in their plans for Multi-Universal domination against Dib and other characters. He worked and served hard for the two but they were defeated and arrested. But they escaped with Slade's scheming and set his new plan into motion where Negaduck nearly dying from Scourge's mistake. They patched things up and went to get his enemy Darkwing and Gosalyn, but Bender found them and defeated them from taking Gosalyn. Things got worse when Joker made his return and was using his subconsciousness as a vessel for torment on everyone until Bender defeated and killed him then Negaduck was back to normal.
Teaming up with Bender and Skipper
Negaduck joined Eddy and the V Team on their adventure where they meet Mordecai, Rigby and Lara Su at the beginning and learned about Uka Uka. Then The V Team learned about Bender and his involvement so they all joined forces to screw Uka Uka. Negaduck had trouble with Eddy since Lara Su was in love with Negaduck instead of Eddy so with help from Mordecai and Rigby it was resolved. Then he and the gang joined up with Bender and they all went for Uka Uka. Negaduck then found love for a traitor in Lien Da and a kinship in Skipper and Bender and he helped the latter two against Uka Uka and helped against the new antagonist Marceline's dad.
Time Traveling experiences
He reappears again and helps the heroes again against Darkwarrior and the return of Joker and Marceline's dad.
After Eggman, Nega, and Turbus are dead, MD Revealed that Negaduck is cheating and captures all of the V Team.
One now wonders what happened to him and the others (minus Eddy, Fiona, Lara Su, Lien Da and Wave). Negaduck was at Slade's wedding with the other members of the V Team and Slade's ensemble. He meets Bender and the B Team (The ones with him for TGSST) and they hang out. Before Bender left to help Eddy and the rest, Negaduck asked him to make sure Lien Da was safe and not harmed, He agreed and told them that they would have a favor to pay him for this. Bender called for that favor and the V Team took back Mobius for Sally and through it he reunited with Eddy and the rest.
Negaduck joins Eddy, Scourge and Nefarious in helping the current Slade and Anti Cosmo against Thawne, after The Joker invades their old lair. He goes with the crew and with pleasure begin tearing up robots when they find The other main members that Slade, Anti Cosmo and Hades have worked with. After meeting some of Slade's new allies he and the three don't know, their capture of The Teen Titans is brought up and that The Joker used his invasion of Slade's base in the past to capture the Teen Titans for his purposes. He brings in his Negamobile which he uses to fight the Arkham Knight when Toffee leads an ambush against Slade's team and captures Slade. Negaduck and the Ensemble find themselves invaded by Deathstroke where Reverb confirms this, He and The rest of the V Team work to find him before he steals the chromoskimmer though he joins his Team to stall Guzma