The story in TMNT: Mutant Melee is based on the 2003 animated series. You play as one of ten characters, each with their own unique abilities, as they battle through a series of opponents in an arena-style fighting game.
The gameplay in TMNT: Mutant Melee takes place in two main modes: single-player adventure mode and multiplayer melee mode. In single-player adventure mode, you guide your chosen character through 100 bouts against enemies or dodging bombs for a set amount of time. Completing these portions unlocks additional characters, bonus characters, and stages for the multiplayer mode.
Melee mode is the core of the game's multiplayer action. It features ten basic characters and twelve unlockable ones, along with nine basic and fifteen unlockable stages. There are four main game types: a knock-out mode where you score the most KOs to win, a Last Man Standing mode where you must be the last player standing, a King of the Hill mode where you defend a glowing patch of ground from other players, and a Keep away mode where you hold a treasure chest and avoid opponents trying to take it.