The Ooze Pit is, as the name implies, a large pit filled with mutagen. At the edge of the pit is a large statue with an open mouth from which mutagen flows. Captives are tied to the statue so that the mutagen can flow over their bodies and transform them. The Ooze Pit appears in both the Turtles of Grayskull (mini-comics) and the Turtles of Grayskull (comics).
Krang and Shredder made a deal with an otherworldly demon mage called Skeletor. In exchange for his dark magic, Krang had been supplying Skeletor with mutagen. The Turtles burst upon the scene to put an end to things, but by interrupting the evil spell, they wound up on Eternia. Upon meeting Man-At-Arms and Teela, the Turtles learned that Skeletor was an old enemy of theirs. Skeletor wanted the power stored in Castle Grayskull, but they had been keeping him at bay for years with the help of a barbarian hero named He-Man.
Having also been sent to Eternia, Krang and Shredder team up with Skeletor, who has added his magic to the mutagen supplied by Krang. This changes the mutagen to a purple mucilaginous substance. Near Snake Mountain, Skeletor sets up a mutagen production quarry which features an Ooze Pit. Skeletor, Krang and Shredder utilize the Ooze Pit to transform henchmen under their control into mutated creatures more powerful than before. The Ooze Pit is also used to transform captured heroes, which places them under the control of their evil masters.