Some TMNT stuff really isn't for little kids.
Slash was an alien anthropomorphic snapping turtle. Originally he lived on a world filled with lush palm trees called Palmadise. Slash's paradise would be shattered when invaders came and cut down all of his his precious trees. Slash soon came across the banished Krang and made a deal to help him back to Earth. Under Krang's leadership Slash teamed with Bellybomb and fought the turtles while Krang sought a new body: that of the Shredder.
Later in the series, Slash went on a rampage in New York and was captured and imprisoned. Newspaper articles drew the attention of the Mighty Mutanimals, who mistook him for one of the Turtles. The Mutanimals broke him out and took the tranquilized Slash back to their island. Once awakened Slash attacked them, until he was subdued by Leatherhead. The Mutanimals were able to calm him enough to allow Slash to explain his backstory to them. He had crashed on earth in New York, and only ceased his rampage when he destroyed a pet shop and took a small fake palm tree from a terrarium, stating that he 'didn't care it was made of plastic.' The Mutanimals informed Slash that he would be allowed to stay on their island home which was filled with the palm trees he so loved. A grateful Slash happily wandered off into the trees, and would become a willing ally of his rescuers.
Later in the series, the Mutanimals were ambushed and gunned down by Null's band of half-dead Cyborgs called the Gang of Four. Slash had not been with his friends at the time, and when the turtles, along with Ninjara, and the future counterparts of Donatello and Raphael were investigating the massacre Slash initially thought the turtles and their friends were responsible and attacked them. Once convinced that the turtles were not to blame, Slash joined them in their investigation. The Gang of Four brazenly confessed to killing the Mutanimals when the two groups fought, sending Slash into a rage. Although he had slain his friends's murderers (with some help), the revelation that Null was behind the attack meant that Slash's quest for vengeance wasn't over.
Tracking Null (and a brainwashed Candace) to Maligna's mobile hiveworld, Slash and his allies fought the Insectoid Queen and her forces. During the battle, Maligna was injured and unable to concentrate on controlling the ship and fight at the same time, causing the hive ship to plummet toward the sun. With Candy rescued, the turtles and their allies were retreating back to their own space ship, but Slash opted instead to stay behind. If the battle came to an end then Maligna would be able to regain control of the hiveship.
The turtles watched from their ship as the Maligna's spacecraft met a fiery demise as it fell into the sun. Although Slash had surely perished, he had put an end to Maligna and the Malignoids and finally avenged his friends.