Some TMNT stuff really isn't for little kids.
Slash is a mutant snapping turtle, originally an experiment of StockGen Inc. and later a founding member of the Mutanimals. While initially a savage and uncontrollable beast, Slash later developed into a caring and complex individual.
He was originally mutated at StockGen in order to track down the Turtles and Splinter, and was known as Specimen 6. As Specimen 6's size and strength increased, his mind became unstable and he turned savage which led him to be contained. He finally escaped when April O'Neil infiltrated the laboratory in order to get rid of the Turtle Tracker, punching one of the Rock Soldiers and departing into the night. As a souvenir of his old life, he took a small palm tree from his old tank.
After his escape from Stockgen's, Specimen 6 lurked around New York as a mindless monster damaging property, scaring and injuring people. He was called "Slash" for the long slashes his claws left. His most prominent attacks were leaving claw marks on April's van, and attacking Michelangelo's pizza delivery friend Woody Dirkins, leaving the man with minor injuries.
Spotting the Turtles, Slash made himself a tattered black mask in imitation of them, and followed them to the abandoned church that they were taking as their new home. He attacked them in the bunker, and his formidable strength was too much for the Turtles to overcome. When Slash was about to kill an unconscious Michelangelo, Leonardo threw a shrunken at him to get his attention, but attempts to reason with the snapping turtle failed. During the struggle, Slash was impaled on one of Leonardo's swords, and fell into the sewer system, washing out to the river. The Turtles presumed that he was dead.
However, Slash did not die of his injury, and was washed ashore to where Old Hob was waiting for him. The mutant cat became responsible for Slash's actions thereafter, and Slash - perhaps understanding that Old Hob had no desire to hurt him - followed him faithfully.
He came back into contact with the Turtles during the City Fall arc, in which he developed a lasting admiration for Michelangelo when the latter gave him a candy bar. He was an integral part of the mission to reclaim Leonardo from the Foot Clan, and developed a strong antipathy towards Hun, whom he knew as the "Dragon Man." At the mission's conclusion, he was given a new black mask by Leonardo, as well as a bladed gauntlet.
Slash's life changed forever when Old Hob began producing new mutants, but discovered that Lindsey Baker's psychotropic compound was crucial to the process. He took a syringe of Splinter's compound-infused blood, declaring that he wanted to be a "hero" like Michelangelo, and injected himself. After a few minutes of agonizing pain, he suddenly began to think more clearly and speak more eloquently than before. With his new intelligence, he became the cofounder of Old Hob's new mutant army, the Mutanimals, and was involved in Hob and Splinter's attack on the Foot Clan.
Another turning point came shortly after Slash's hero Michelangelo was briefly inducted into the Mutanimals, much to Slash's delight. However, he was horrified to discover that Old Hob had been stockpiling weapons and had hired Hun to handle the matters for him. As a result, he broke ties with the Mutanimals, despite his enduring fondness for them. When Michelangelo offered to let Slash stay with him in his family's old lair, Slash declined, saying that he needed to spend some time as his own master, but that Michelangelo would always be his hero.
Despite striking out alone, Slash reunited with both the Mutanimals and the Turtles the following Christmas. He brought an assortment of candy bars, and terrified Woody Dirkins despite his now-friendly demeanor.
He continued his solitary exploration of New York, but was unaware that he was being tracked by the Earth Protection Force and Dark Water. They captured him while he was reading on a rooftop, collapsing the building in order to stun him, and implanted control nodes that allowed him to be used as a weapon by Agent John Bishop.
Bishop immediately turned Slash against the Mutanimals, violently attacking them and allowing the E.P.F. to capture them as well. While the Mutanimals were eventually freed by the efforts of Old Hob and the Turtles, Slash remained enslaved by Bishop. He was later used against the Triceraton landing party during Bishop's first contact with them.
It seems more and more that it's become far too easy for us to sacrifice the good in order to confront the bad. The others may not see this as Mikey and I do, but they've never suffered Hun's venom the way we have. You've invited a serpent into the garden, Old Hob... ...and that is something I simply cannot abide by.
My whole life, I've felt like someone else's property. First I was Stockman's lab experiment, then later, despite his best intentions, Hob's plaything. After all the amazing changes I've gone through, that feeling of inadequacy has never left me and I think it's past time I venture out on my own and finally learn what it is to be my own master. But before I go, I want you to know, Mikey, you have always been—and will always be—my hero. Farewell, my friend.