The Creep is a mutant that debuted in the episode "Within the Woods".
- Within the Woods: While recovering from the defeat from Shredder, Leo spends some time recovering in North Hampton, New York. When Donatello creates medicine from Mutagen Ooze|Mutagen for his brother, he vomits it up back into the bog, creating The Creep. The Creep kidnapped Raphael turning him into a "puppy" made of moss. He also kidnapped Michelangelo, Donatello, Casey Jones, and April forcing Leo to come to aid. He was defeated by the turtles and put in a jar. The episode ends with the jar glowing and beginning to crack.
- The Creeping Doom: The Creep was accidentally brought back to life by Mikey, when Mikey bumped into a shelf causing several items, including Creep's jar, to fall. The Creep's remains mixed with a mind control antidote that Donnie was working on, which not only revived the Creep but also made him smarter. The Creep then stole Snakeweed's claw from Donnie's lab, attacked the Turtles, and escaped the lair. Later, the Creep used his mutagen-siphoning powers to make a Snakeweed clone from the claw, which Mikey dubbed "Son of Snakeweed." The Turtles tracked down Creep and destroyed both mutants. But the resulting mess caused the Creep and Son of Snakeweed to fuse together and become a super-mutant Mikey named "Creepweed." Creepweed began attacking New York City, capturing people and trapping them in plant pods, similarly to how the original Snakeweed did in the episode New Girl in Town. Donnie defeated Creepweed by spraying retromutagen in its mouth, causing it to explode.
The Creep is made of mud, grass, and swamp water. He wears "Vorhees" bran overalls and Casey's Mask|hockey mask, that he stole from Casey. His eyes and mouth also glow Turquoise.
- On the concept art, it says "Show 301". which means he debuts in Season 3 Episode 1.
- The Creep is the second plant-like mutant with regenerative abilities to be introduced in the series; the first being Snakeweed.
- Like Snakeweed, he appears in the first episode of the season. This is ironic because both are plant creatures and they appeared in the first episode of a season.
- He in an obvious reference to Friday the 13th's Jason Voorhees.
- The Creep uses a bag with only one eye whole as a mask, but later he trades it for a hockey mask, much like Jason Voorhees.
- His overalls read "Vorhees".
- The shrine he has of the mutagen mirrors the shrine to the head of Jason's mother.
- Both the Creep and Jason Voorhees don't talk, only grunt.
- The Creep wears a hockey mask that he stole from Casey.
- The Creep stole Raphael's mutagen just like Bloodsucker did in the Mirage comics.
- Leo's mutagenized vomit created the Creep. Leo's vomit is also the same substance of his blood.
- This is the first mutant Mikey has named in a while. Last being Pizza Face.
- He tries to wear everything on his head meaning he thinks his face is ugly.
- He has the power to drain mutagen out of a mutant's body.
- He also has the power to put mutagen into the body parts of plant-based mutants to make clones of them.