[s2e1] | The Mutation Situation

The Turtles celebrate their victory over the Kraang from the Season 1 finale, but the peace is short-lived. They discover that Shredder has formed an alliance with the Kraang to obtain a fresh supply of mutagen. During a high-stakes interception on a Kraang stealth ship, a mishap causes dozens of mutagen canisters to be scattered across New York City.

Shredder begins looking for new recruits to bolster his forces, eventually leading to the creation of his own mutant army. Where to Watch [S2E1] The Mutation Situation

Though they feature more heavily in later episodes, the mutation fallout begins here. The Turtles celebrate their victory over the Kraang