Plasma is a creature made solely of positive ions and electrons. Manifested by the control box held by Arnem Abacus, Plasma was ordered to guard the prisons of the Metropolis Zone to ensure the prisoners were taken to a Badnik Processing Plant. His attentions turned to Sonic the Hedgehog when Sonic, Amy Rose and Johnny Lightfoot broke the citizens out of jail. Being made of energy, Sonic found it impossible to touch Plasma, yet could be subjected by Plasma's energy attacks. He was eventually defeated when Amy attacked Abacus and destroyed the control box.
Plasma was revived by Doctor Robotnik when he was a God, but the creature still needed Abacus to keep him alive. It was the collision between himself and Commander Brutus that condemned himself and his villainous colleagues to an early grave. In this guise, Plasma had white eyes, as opposed to his earlier red-eyed appearance. He returned one more time (with red eyes) as a foe summoned by Violet Witchbrew to terrorise her native Hill Top Zone. Sonic and Tails prepared to fight Plasma (and many other enemies) but Plasma was erased by Agiatha Witchbrew. Arnem could not be seen this time, although he may have been obscured by a Trooper blockade.
A sentence of graffiti appeared on a pin-up in the Christmas Special 2012, quoting Plasma's "I am Plasma, master of electrons" quote in his original story. Its appearance suggests that Plasma may have been revived during Robotnik's new invasion of Mobius. This theory was given more ground when a poster of him appeared on the side of a skyscraper in the Metropolis Zone.