Retromutagen 216

First Appearance

The Lonely Mutation of Baxter Stockman

Last Appearance


Known victims

Mr. O'Neil, Citizens of Manhattan (to full extent)

Karai (to half extent)

Known attempted victims

Rahzar, Stockman-Fly, Bebop, Rocksteady

Retromutagen is a chemical that can reverse the effects of the notorious Mutagen Ooze. It has the power to undo every mutation and turn a human Mutant (like Kirby Bat) human again. It can also turn an animal Mutant (like Spy-Roach) back to a regular animal. In several episodes, Donatello is seen trying to make this substance, but fails twice.

The Lonely Mutation of Baxter Stockman: Donnie finally completes the formula, and turns WingNut back into Kirby.

Serpent Hunt: It's revealed that Donnie had been making when he was at the farmhouse, but it still might take a while.

The Pig and the Rhino: The Turtles hunt for Karai to give her the finished retromutagen, and have to stop Bebop & Rocksteady from stealing said cure.

Battle for New York: Due to Mikey messing with some of Donnie's chemicals, he manages to create a serum that one drop of it can make a whole vile of mutagen instantly turn into retromutagen. This makes it easier for Donnie since he used the same serum to instantly turn all of the mutagen in one of the Technodrome into retromutagen to turn all of the Kraangatized people back to normal.


  • The past retromutagens have failed for different types of reasons.
  • It is revealed in The Lonely Mutation of Baxter Stockman that it took ten canisters to synthesize the correct formula for the retromutagen, and April O' Neil's DNA is one of the requirements needed to make it.
  • A possible side effect of the retromutagen is no memory of being a mutant.
  • It's unknown if Donatello will make more or he was just making it for Kirby O'Neil. Seeing as though he promised Timothy he would turn him back and was hoping to make some more for Karai, it's likely he will try to make more.
  • Playmates released mutagen ooze with different color variants one being orange which possibly foreshadowed the retromutagen.
  • Seemingly, when Mutagen is mixed with retromutagen, whoever it mutates will be able to shapeshift back into their human form but will still have a few traits of their mutant form. (ex. Karai)
  • The retromutagen is the same color as the Nickelodeon logo.
  • Just one drop can cure a mutant.
    • This makes a major inconsistency in the events of The Lonely Mutation of Baxter Stockman and The Pig and the Rhino. Given how much retromutagen was in each episodes' containers, they shouldn't have to fight over who gets it. Then again, Shredder's henchmen are known to be just as selfish as any villain so they probably just didn't care.
  • Mikey made a Super-Retromutagen that can turn mutagen into retromutagen.
    • The ingredients of the Super Retromutagen are a few tubes of sodium bicarbonates, a skeleton of a fish, an eaten apple and half of slice of garlic cheese pizza.
    • Since Karai is immune to the normal retromutagen, it may take a special ingredient to cure her.
  • This was a rare creation of Mikey's that turned out helpful.
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