Tooth Decay is a monstrous being who appeared in "Royal Pudding", where he appears as the main antagonist. He is a literally monstrous portrayal of the condition tooth decay, the breaking down of teeth due to acids created by bacteria.
He kidnapped the princess, and all the Canadians rose up to try to save her in a state of national emergency. Scott the Dick, Ike Broflovski, Ugly Bob and some Eskimos manage to find the princess. Ike kills Tooth Decay using Bob's ugliness, turning him into stone and saving the princess.
In the kindergarten play, while Ike is absent, Kyle Broflovski is forced to play the role of Tooth Decay, and Mr. Mackey is very disappointed by his lacklustre performance. Making the play was a cathartic experience for Mr. Mackey, who lost his father to Tooth Decay several years ago.
Tooth decay appears as a hideos and terrifying huge green monster covered in spikes, with glowing yellow eyes.
- When Tooth Decay sees Ugly Bob's face, it turns to stone, but when Terrance and Phillip see Bob's face in "Terrance and Phillip in Not Without My Anus" they are not affected.
- His death is a parody of the Greek mythological figure Perseus, who apparently showed the decapitated head of the Gorgon Medusa to the Kraken, turning it into stone.