Teenage Mutant Ninja Turtles: Ultimate Mutation is the best web American animated series, mainly set in New York City. The trailer reveals the turtle's new voices, the animation, and that the theme song of the new show will be a remixed/remade version of the original theme song from the 1987 cartoon. The Brang combines elements of both Utroms and the Kraang. Ultimate Mutation is not based on the 2012 series, but exists in its own "hyper realistic 3D-style" world inspired by the 2012 show.
When ninjutsu master Hamato Yoshi and his four pet baby turtles are exposed to mutagen (a chemical from another world that transforms anyone who comes in contact with it into mutant creatures), they undergo major physical transformations: Hamato Yoshi becomes a humanoid rat under the name of Splinter and the turtles become human/turtle hybrids. Splinter retreats to the New York City sewers, where he raises the four turtles as his sons and imparts to them his knowledge of ninjutsu.
After venturing to the surface for the first time, the teenage Turtles discover an alien race called the Brang is planning to take over New York City with their plans involving the same mutagen that created the Ninja Turtles. The Turtles befriend the teenage April O'Neil when she and her father Kirby have been abducted by the Brang alongside some other captive scientists. While Kirby remains a prisoner of the Brang, April becomes an ally of the Turtles as they help her to find out where the Brang have taken her father.
- Teenage Mutant Ninja Turtles - A team of anthropomorphic freshwater turtles who are the protagonists of the series:
- Leonardo - "Leo" is an enthusiastic student, learning how to be an effective leader for his three often unruly brothers. He wears a blue mask and fights with two katana swords called Niten Ryu. Aside from his sensei, he takes leadership references from his favorite sci-fi series Space Heroes which annoys Raph to no end.
- Donatello - "Donnie" is in charge of the design and manufacture of all of the tools and weapons in the Turtles' arsenal, and he is also a gifted hacker. He wears a purple mask and fights with a rokushakubo which converts to a naginata. He also has a crush on April which his brothers all tease him about. This incarnation of Donatello is depicted with freckles and a gap with braces.
- Raphael - "Raph" often lets his impulsiveness get in the way of rational thinking. He wears a red mask and fights with two sai. This incarnation of Raphael is depicted with a lightning-shaped scar on his left eye.
- Michelangelo - "Mikey" loves video games, skateboarding, pranks, comics, horror movies and pizza. He wears an orange mask and fights with two nunchaku, which convert into kusarigama.
- April O'Neil - The 16 year-old daughter of Dr. Kirby O'Neil who likes to play video games and eat pizza. April befriends the Turtles after the Brang kidnap her and her father. After the Brang get away with her father, April's aunt takes her in and the Turtles promise to help her find her father and take down the Brang.
- Hamato Yoshi/Splinter - Splinter was originally the human Hamato Yoshi and resided in Japan where he became an expert of ninjutsu. When his friend Oroku Saki sought the affections of Splinter's wife Tang Shen, Saki wished to discredit Yoshi in front of her. Yoshi lost his temper and the altercation ended their friendship culminating in a battle that burned down Yoshi's home killing Shen and their daughter Miwa. After moving to New York City, Yoshi had just purchased four pet turtles when he stumbled upon an exchange in an alley between two Brang droids. Seeking to silence Yoshi before he could share what he had seen, a fight ensued and the canister the droids had been carrying smashed open splashing both Yoshi and his turtles with an alien chemical called mutagen. As the result, Yoshi changed into a humanoid rat after having had contact with a rat upon entering an alley. Realizing he could no longer live a normal life topside, he retreated to the New York sewers where he raised his pets as sons and taught them the ancient Japanese fighting art of ninjutsu. Unlike the previous animated series, the Turtles often refer to Splinter as their father, rather than their master.
- Foot Clan - A ninja organization that is led by the Shredder.
- Oroku Saki/Shredder - One of the primary antagonists of the series and leader of the Foot Clan. Once friends in Japan, Oroku Saki and Hamato Yoshi parted ways when both fell for Tang Shen who ultimately chose Yoshi. Saki's jealousy turned to anger and hatred, especially after Yoshi and Shen welcomed a baby daughter named Miwa. A final battle resulted in a fire that burnt down Yoshi's home burnt part of Saki's face, and killed Shen and Miwa. Oroku Saki became the Shredder and established the Foot Clan. Years later, Shredder learns that Splinter is alive and in New York after seeing the Hamato clan crest on a shuriken during a television news report. Seeking to finish his business with Splinter, Shredder and his Foot Clan relocate to New York. The Turtles first encounter Shredder in "The Gauntlet" where he dominated them all in combat. Shredder almost kills Leonardo, but the distraction of the newly-mutated Scarface and Greg Krafford gave the Turtles the chance to escape. In the same episode, Shredder is shown to have a pet Shikoku named Jinkaku. He is also Karai's father as seen in "New Girl in Town." In "The Alien Detective", Shredder didn't believe in the Brang until Karai brought him the robot body of one of the Brangs. As Baxter Stockman gets to work on studying the technology, Shredder assigns Karai to learn more about the Brang so that he can use whatever information is gathered about them in his war against the Turtles.
- Karai - A rebellious teen member of the Foot Clan and an expert kunoichi who stirs up trouble for the Turtles.
- Hun - Shredder's right hand, and leader of the Purple Dragons, an urban street gang that Shredder sometimes utilizes. He constantly seeks the Shredder's approval and leads the Foot into battle against the Turtles. He is a large, hulking bully, powerful but fast and very skilled in martial arts.
- Greg Krafford/Meandog - Greg Krafford was a famous martial artist (who is modeled after Georges St-Pierre) and secretly a member of the Foot Clan. Greg Krafford is ordered to New York with Scarface to find Splinter. In "The Message", Krafford and Scarface go after the Turtles again and are exposed to mutagen. As Krafford was previously bitten by Shredder's pet Shikoku, Jinkaku, the mutagen transforms him into Meandog, a spike-backed dog-like mutant with a large arms, heightened senses, and super-strength.
- Scarface/Snakehead - Scarface was a Venezuelan street thug. He was in a prison until Shredder freed him and indoctrinated him into the Foot Clan. Shredder orders this ruthless, accomplished fighter to assist Greg Krafford in finding Splinter. In "The Message", Scarface is exposed to mutagen. As Scarface previously touched a red spitting cobra at a pet store, the mutagen transforms him into the snake-like mutant Snakehead.
- Foot Ninjas - The foot soldiers of the Foot Clan.
- Foot Elite - The foot warriors of the Foot Clan served as the bodyguards and field leaders.
- Foot Techs - The foot technicians of the Foot Clan.
- The Brang - One of the main antagonists of the series. The Brang are a race of brain-shaped aliens from Dimension X that pilot robotic bodies and are responsible for bringing mutagen to Earth. The Brang have mastered English and communicate in redundant speech.
- Gnarb - Gnarb is a ruthless leader of the Brang. As second-in-command of the Dimension X, he served under his father, Supreme Commander Krang. His name is "Brang" backwards.
- Krang - Krang is a more intelligent supreme commander of the Brang.