Some TMNT stuff really isn't for little kids.
As a child, when he did chores for a Native American man and his granddaughter, Raven Shadowheart, the human who would become Complete Carnage made the mistake of violating sacred ground, placing a curse on himself that would one day catch up with him (TMNT Vol. 1, #27). His origin story describes that he started out as a regular human construction worker. One day while he was fixing a cement wall, he was struck by lightning. This mutated him and turned him evil. The same lightning bolt also hit Raven Shadowheart when she was jogging in Central Park. She became "Radical" and represents ultimate good. He represents ultimate evil. They became arch-enemies.
He has the power to move steel and concrete and absorb energy from said things. He can also walk through steel and concrete. Upon his first appearance in Tales of TMNT Vol 1 #5, it is mentioned that he used to be called "Carnage" but now due to his true understanding of his powers, he refers to himself as "Complete Carnage."
One of Radical and Carnage's earliest confrontations occurred when Casey Jones and Raphael stumbled into him while entering a building they thought abandoned. Radical appeared and, after a short fight, flung him with enough power to send him halfway across the world (Shell Shock). Bouncing off a 747, Carnage crashed into the temple of the Holy Order of Zentaoists, a religious cult located in the upper New York state. Received as a prophet, the cult taught him of his hidden abilities. Now possessing the ability to freely pass through and absorb into man-made things, he posed an even greater threat to Radical. Another confrontation occurred when Carnage appeared when she was biking, surprising and nearly overtaking her. Pulling off his arm, Radical lured him away with the help of the Turtles, then used her "Particle Beam" ability, warping them to the ethereal-like "Dreamscape" (Tales of the TMNT #5). Radical and Carnage sparred for the final time when she sought out Carnage, having the Turtles distract him while she prepared a spell that liquefied the road Carnage attempted to dive into, liquefying (and killing) him in the process (TMNT Vol. 1, #27). It seemed the arm Radical pulled from Carnage's socket fell into the hands of the Whelan-Freas Scientific Research Center. The center generated a clone of Carnage from the arm, a clone that escaped to go on a rampage in Chicago. The Turtles, learning of this, sought Radical's help. She was unable to intervene against Carnage because she did not have permission from the "council," (because the creature rampaging was a clone, not the real Carnage—the being she was destined to fight and had already beaten) but the Turtles were victorious nonetheless with the help of Officer Dragon. Flung far and deep into Lake Michigan, the cloned Carnage was drowned by one of the Dragon's deadliest foes, the Fiend (TMNT/TSD II & TSD series #22).
- The non-canonical Palladium Books role-playing game Transdimensional Teenage Mutant Ninja Turtles lists Complete Carnage's human name as Max Wilsocchi. This name does not appear in any of the Mirage comics.