Description:

- A mutant was any being who had been affected by mutagen
- Mutagen was a gelatinous chemical substance from Dimension-X

Known Mutants:

- Donatello (Mutant Turtle)
- Leonardo (Mutant Turtle)
- Michelangelo (Mutant Turtle)
- Raphael (Mutant Turtle)
- Hamato Yoshi/Splinter (Mutant Rat)
- Bebop (Mutant Warthog)
- Rocksteady (Mutant Rhinoceros)
- Scrag (Mutant Bat)
- Mondo Gecko (Mutant Gecko)
- Muckman (Garbage Mutant)
- Napoleon Bonafrog (Mutant Frog)
- Genghis Frog (Mutant Frog)
- Rasputin the Mad Frog (Mutant Frog)
- Attila the Frog (Mutant Frog)
- Slash (Mutant Turtle)
- Mona Lisa (Mutant Salamander)
- Leatherhead (Mutant Alligator)
- Tokka Mutant Snapping Turtle)
- Rahzar (Mutant Wolf)

Highlights:

- Mutants took on the traits of the things they transformed into:
- Like animals taking on human traits or humans taking on animal traits
- On rare occasions, beings could be mutated into objects:
- Like living garbage or even just a mess of living organs
- Exposure to Mutagen without contact with anything: turns you into a mutant blob