Mutagen, also known as Mutagenic Ooze, is a mucilaginous substance that has served as a key plot device in nearly every medium of the Teenage Mutant Ninja Turtles. Any creature that is exposed to mutagen will be effected in a myriad of ways, from growing in size and mind, merging with inorganic materials, or gaining superpowers such as telepathy or telekinesis. It is responsible for mutating, among others, Splinter, the four turtles, and villains such as Rahzar and Fishface.
In this series, the Mutagen is depicted as having several similar properties to the version seen in the 1987 series; It blends with the victim's genetics with that of whatever creature they have last made contact with. It has a glowingly blue/green coloration to it.
Cockroach Terminator - The Mutagen also has the ability to merge organic substances and inorganic substances, as seen with Spy-Roach, and the same subject shows that it can also cause similar effects to the original comic version, both increasing size and intelligence sometimes.
The Pulverizer Returns! - The Kraang operative told Shredder that the effects of the Mutagen on Earth are unpredictable. If a human has not come into contact with another living being before being effected by Mutagen, their bodies will be molecularly broken down, turning them into a mutant blob made of acidic goo, with only their internal organs still remaining intact. Pulverizer also states that the Mutagen burns a lot.
Mikey Gets Shellacne - Exposure to a secondary dose of mutagen can accelerate the original mutation; when Bradford (As Dogpound) falls into a vat of mutagen, he is further mutated into a new form known as Rahzar.
The Kraang Conspiracy - It has been stated that the mutagen was not intentionally created as a mutative agent, and apparently had a different effect back in Dimension X, but the new laws of physics in our dimension altered it's function.
The Lonely Mutation Of Baxter Stockman - It is revealed that April is immune to mutagen.
Into Dimension X! - In this episode, the Kraang perfected the mutagen, revealing it's true purpose; to "terraform" Earth into a new Dimension X. Objects such as rocks or trees sprayed with the perfected mutagen transform into Kraang elements and creatures including humans are mutated into Kraang monsters.
City at War - Stockman-Fly started feeding mutagen to Shredder while he was recuperating.
The Insecta Trifecta - The mutagen that was injected into Shredder started to take it's effect where he started to sprout razor-sharp blades from the back of his hands.
The contact with mutagen causes one to merge with the DNA of the last creature one came in contact with, if one has not recently came in contact with any living being it causes one to mutate into a undefined blob. For Example, Timothy.
It is shown that when exposed to inorganic matter such as cement, it causes it to dissolve like an acid, considering Timothy explained that mutagen burned him, mutagen in its base form might just be an acid.
If one is physically hurt when mutated, the wound will reflect on its final form. For example, Chris Bradford was bitten by Shredder's dog on his right hand, as a consequence Bradford's wounded arm did not grow as it should when he transformed into Dogpound.
If ingested the mutagen causes one to mutate into the last thing ingested before the mutagen. For example, Antonio mutated into Pizza Face as pizza was the last thing he ate and a nameless cat mutated into Ice Cream Kitty, as she ingested a mix of mutagen and Ice cream.
- The only known exception are the Squirrelanoids.
Oddly, the mutagen causes some subjects to lose their intellect in some cases. For example, Dr. Tyler Rockwell and Dr. Kirby O'Neil who became the instinctive beasts "Monkey Brains" and "Kirby Bat", respectively.
In some rare occasions when an animal hasn't recently come in contact with a human, the exposure to mutagen causes is to develop a human level intellect as well as an anthropomorphic mutation. For example, The Punk Frogs.
The effects of fusion are similar to the regular exposure, the main differences being that, as the name implies, fusion merges two or more living creatures instead of just mutating one based on others DNA. For Example, Mega Shredder and Creepweed.
- It can also cause the merging of organical with inorganical matter. For example, "Cockroach Terminator", which is the fusion of a cockroach and spy equipment.
Until now, second mutations are known to cause, as referred by Mikey, "super mutants". It happens when a mutant is exposed to mutagen for a second time. The only known example of super mutation is Rahzar, an evolved version of Chris Bradford's first mutant form.
Monkey Brains - Dr. Victor Falco produced a specific version of the mutagen that would not only mutate Dr. Rockwell but also give him psychic powers, later Falco perfected the serum, giving him the ability to read minds.
I, Monster - While using rats to test his psychic serum, Falco suffered an accident that gave him new abilities.
Parasitica - Donatello stated that the mutagen effects are usually anthropomorphic, which is not the case of the parasitic wasp, that suffered a increase in size.
The Lonely Mutation of Baxter Stockman - Donnie develops a cure for Kirby and Splinter's mutations, this time called Retro-Mutagen. It takes about ten canisters of mutagen, April's DNA, and several months to create one small dose of antidote.
Vengeance is Mine - Stockman accidentally modifies the mutagen that mutated Karai, making it possible for her to shift back into her human form. As was revealed later in The Pig and The Rhino, this unique mutation can not be reversed by using regular Retro-Mutagen.
Within the Woods - Donatello creates a mutagen based medicine for Leo, "Leo's Elixir" did not mutate him, but once it was out of his body it caused the Creep's mutation. The Creep worships the mutagen and had an altar for Leo's Elixir.
Race with the Demon - Speed Demon spills some Mutagen Gasoline on the road, which later causes the mutation of Dr. Cluckingsworth M.D., who's able to lay Radioactive Mutagen Eggs. Donnie and Casey use the eggs as fuel for the Turtle Racer.
Battle for New York, Part 2 - Michelangelo accidentally created a super retro-mutagen formula that can transform huge amounts of mutagen into retro-mutagen. The Turtles stole a Technodrome and used its mutagen tank to unmutated the whole population of New York, including Kirby.
In the beginning of second season Donatello developed devices that would help him and his brothers to look for the missing mutagen canisters.