Speed Demon is a mutant muscle car that turns whoever drives him into a mutant driver that is thirsty for high speed. The Concept Art and 3D model for Donnie's possessed form was revealed at the NYCC 2014 panel.
The Croaking - At the end of the episode, we see a purple muscle car passing through the Punk Frogs' sacred Mutagen that Rasputin the Mad Frog had lost during the Punk Frog's fight with the Turtles spilled on the road.
Race with the Demon- It pursues Donatello, April O'Neil, and Casey Jones in their station wagon and tries to run them off the road. News of the Demon Racer's vehicle causing trouble on the road reaches the local news. In order to get even with the Speed Demon, Casey and Donatello construct a racing vehicle to compete with him. Casey later encounters the Speed Demon's vehicle where he finds that Speed Demon is actually a mutant. When Speed Demon plans to run an old lady and her vehicle off the road, Casey repelled the Speed Demon just as the Ninja Turtles catch up. Michelangelo found Mutagen on the road that leaked from the Speed Demon as Donatello claims a sample of it. While piloting the new car (which was made from parts of Kraang technology) with Dr. Cluckingsworth, Casey works to take down Speed Demon by useing a smokescreen to slow it down. Donatello removed the driver from the car, who restores to normal. . Donatello learns too late that the car is the actual mutant as Speed Demon possesses him. In order to get Donatello out of Speed Demon, Casey ends up in a race to Dead Man's Curb for the fate of Donatello. With help from Dr. Cluckingsworth, Casey frees Donatello from Speed Demon as it starts to attack them. After the other Turtles arrive and run Speed Demon off a cliff, he vows to return before exploding. However, in Eyes of the Chimera, it's revealed that the explosion released Mutagen that ended up creating the Chimera.
- Speed Demon resembles 1983 John Carpenter's horror film Christine, which is about a sentient and violent automobile of the same name.
- The Speed Demon makes stock monster laughter when he crashes
- His license plate reads DEMON.
- The human the speed demon possessed has hair and clothes similar to a stereotypical 60's car jockey.
- The Speed Demon Donnie highly resembles Rat Fink and other characters created by Ed Roth.