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 which drew the attention of the Mighty Mutanimals. After he was captured and imprisoned the Mutanimals broke him out and took him back to their island. Once awakened Slash continued his violent spree until subdued by Leatherhead. Now in a somewhat more peaceful state, the Mutanimals were able to calm him enough to inform him that he would be allowed to stay in a grove of lush palm trees he so loved. A grateful Slash strode off happily and would become an 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 Candy) 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, but Slash opted instead to stay behind. If the battle came to an end then Null and Maligna would be able to regain control of the ship.
The turtles watched as the 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.