Shredder and the Kraang team up! Now as a combined force, the Turtles face double the threat! But the ultimate shell-shocking surprise occurs when a supply of mutagen canisters are accidentally released into the city by none other than the Turtles themselves! With mutagen ooze on the loose, the Turtles set out to find the canisters before they fall into the wrong hands...and in some cases, they may be too late! More mutagen means more mutations! Enter Kirby Bat, Squirrelanoids, Mushroom Men, Slash, and more! With new mutants lurking throughout New York, and the return of evil villains including Karai, the Rat King, and Foot Bots determined to take down the lean, mean, green team, get ready to join Leo, Raph, Mikey, Donnie, April, and new ally, Casey Jones, as they fight back and take the ninjutsu battle action to new rooftop heights!