Anti-Sheldon Plankton

Anti-Sheldon J. Plankton, or simply Anti-Plankton, was a villainous plankton from the Anti-Characters Universe.

Biography
Years after witnessing his father murder his mother when he was a child, Plankton became a serial killer.

Following the B.A.S.I.C.S. Labs explosion, Plankton was affected during electroshock therapy by the dark magic involved, giving him speed and various other abilities derived from it.

Following this, he escaped and began acting as a supervillain known as Fatdi, stylized as the Fast Wraith.

Later, using Acceleration serums, Plankton managed to artificially increase his speed to the point where he could break the dimensional barrier.

Having gotten tired of being the villain, Plankton decided to become "the hero" as Antonio Sea/InstAnt, stylized as the Crimson Ant, borrowing the name and claimed species from the insect superhero he found in another universe and kept as prisoner.

He created the charade in order to instill false hope - hope that would be ripped away.

Discovering the existence of B Frit in TPUWCPADOSU, Plankton traveled to the other universe and acted as a friend and mentor, apparently training to fight Fatdi, but actually planning to increase B's speed to eventually take it for himself.

Plankton eventually killed a timeline echo of himself to give B a reason to avenge "Antonio" and increase his speed even further, only for his true identity to be discovered by Team InstAnt soon after.

Shortly after, intending to break B emotionally, he murdered Gordon Frit, thus being indirectly responsible for B's timeline change.

After losing a race to B and attempting to destroy the multiverse, Fast Time demons appeared and imprisoned Plankton in Fast Time, while reducing him to a decayed spectre-like form known as Black InstAnt.

He returned a short time later in the post-InstAntpoint timeline as a mindless being bound to the will of Fast Time for all eternity, while hunting down a timeline echo of Hornet Wings who existed in the new timeline due to InstAntpoint, but was not supposed to exist because of ancestor Sting Wings' suicide.

After Wings and the Never Existing Villains assembled the Spear of Fate and changed reality, Plankton was held captive by Wings in B.A.S.I.C.S. Labs.

After the timeline was restored, Plankton chased down a future version of Wings who had traveled to 1917 Lanoka to ensure the Space Myths wouldn't stop him from altering reality with the Spear of Fate, and killed Wings, also erasing all of Wings' timeline echoes.

He was later sent after Arunasura as the timeline echo tried to send fragments of himself through time using Fast Time, only to be frozen and shattered by Killer Silo.

In the creation of the new multiverse, Plankton's history was re-written, where he was apparently from Earth-Gravildus-Batorok instead and marched on Bugtown with his terrifying army. However, much like the original multiverse, he was ultimately defeated by Team InstAnt.

Trivia

 * Unlike most Anti-Characters, he is even more evil than his NES counterpart, rather than being oppositely so.