This unknown child, having grown up in the town of South Park, became sick of seeing crime and evil in his community, and the incompetence of town's police forces. As violence and darkness took over the streets, he works, sometimes alone, to rid the streets of crime. He is the symbol this town needs. A watchful protector. A silent guardian. An agnostic angel.
He was first sighted publicly the same week the Coon made his debut, and sparred with him and Professor Chaos before being arrested as a vigilante. He later joined Coon and Friends and helped with the Gulf Oil Spill crisis with Captain Hindsight and Mint-Berry Crunch, revealing his super-power though struggling to come to terms with it. In some times of distress, he also comforts his sister under the guise of his alter-ego.
Although his identity remained a mystery for a long time, he was finally to be... Kenny.
- "I'm an angel keeping watch over the city at night. As violence and darkness take over the streets I work to rid this city of crime. I'm the symbol this town needs." (The Coon)
- "I assume you must be Cartman, because you are fat." (The Coon)
- "Kyle Broflovski hates Eric Cartman. Are you saying you're Eric Cartman?" (The Coon)
- "Pull the trigger, Hindsight - if you don't believe us, then you don't have a choice. Pull the trigger, you pussy!" (Mysterion Rises)
- "I can't die. I've experienced death countless times. Sometimes I see a bright light, sometimes I see heaven or hell. But eventually no matter what I wake up in my bed wearing my same old clothes. And the worst part? No body even remembers me dying. I go to to school the next day and everyone's all "Oh hey, Kenny.". Even if they've seen me get decapitated with their own eyes. So you want to whine about curses, Hindsight? You're talking to the wrong fucking cowboy." (Mysterion Rises)
- "Do you know what it feels like to be stabbed? Decapitated? Torn apart? Burned? Run over?" (Coon vs. Coon and Friends)
- "Sometimes, people do stupid things, sometimes they don't think of what should've come first - until it's too late." (The Poor Kid)
- "Don't try, Karen. Do." (The Poor Kid)
- "Karen McCormick is off limits! Do you understand? Make sure everybody in this school knows!" (The Poor Kid)
- The Coon (s13e02; debut)
- Coon 2: Hindsight (s14e11)
- Mysterion Rises (s14e12; identity revealed)
- Coon vs. Coon and Friends (s14e13)
- The Poor Kid (s15e14)
- In a fan poll conducted by South Park Studios in the week between "Coon 2: Hindsight" and "Mysterion Rises" airing, most fans agreed that Kenny was the most likely person to be Mysterion. Clyde Donovan came out as a distant runner-up.
- Kenny's interest in comic books was also shown in "Sexual Healing", when he died via auto-erotic asphyxiation wearing a Batman costume. He also takes the lead when the boys form The Avengers, as Iron Man.
Mysterion is a playable characters in the XBLA game, South Park: Tenorman's Revenge, if one is playing as Kenny.
- Special Attack - can 'die' and then continue moving past obstacles that would normally kill other characters.
Mysterion's costume can be found in Kenny's closet, unused. He was originally going to be one of his special moves in the game but was cut for unknown reasons.