The mutant turtle is the second boss, fought in the final area of "Chapter 2: The Sewers".
The mutant turtle has mint-green skin, with a darker shade of green for its shell. Its two white eyes are unevenly sized, and it has a gaping red mouth, with one tooth on each corner. Its bent knees have three visible claws on each foot. On the shell, the mutant turtle wears a silver belt with a spike that rests on top of the shell. On either side of the spike, there is a tube-shaped cannon.
When the player reaches level twelve, they will encounter the mutant turtle. The area is enclosed, with the hero on the side closest to the door and the boss on the opposite platform. Both elevated platforms are separated by a pool of water.
The mutant turtle remains stationary for the entire duration of the battle. During the fight with the hero, it retracts its head every few seconds and fire a continuous stream of bullets, which fly in an arc towards the direction of the hero. The turtle then pokes its head out from hiding. At this point, it is vulnerable to the bullets from the hero's gun.
Unlike the muscle zombie or horned zombie, the mutant turtle can only be hit when it is not firing at the hero. When its head is visible on screen, the player should constantly fire at it from the platform on the other side of the turtle.
As the turtle retracts its head to fire bullets, the player should move the hero around the area to avoid being hit by the oncoming bullets. Gaps between fired bullets are sometimes briefly left, of which the player can take opportunity to switch directions of the hero. Since water slows the hero down, he is prone to the continuous stream of bullets.
Once the turtle's health is fully depleted, it will erupt in an explosion before disappearing off screen. The level then transitions to the cemetary area and the player will receive the "Teenage Mutant Boss Turtle" achievement if they defeat the mutant turtle for the first time.