He was nine, and revealing his identity hadn't impacted his life as much as he would have expected. It was in the newspaper and mentioned on the news, but it turned out there really weren't all that many kids at school who paid attention to either of those. Wendy, who'd never really paid much attention to him even when they were both hanging around Stan at the same time, stopped him with a smile to let him know she thought the things he'd done were really great, and for a few weeks Kyle picked him instead of Stan whenever everyone had to pair up for a school assignment, but that was the only change. For a little while everyone kept gossiping about who Mysterion could be like it was still a mystery, then time passed and they all just seemed to forget about it.
Mysterion only came out when his parents needed a quick reminder that someone was watching them, or Kevin looked like he might be falling into the same type of bad habits they had and needed to be scared back onto the almost straight and narrow, or he heard Karen crying herself to sleep and appeared to comfort her. Small, personal acts of heroism that no villain would ever care about, or even notice. Aside from that he was fully prepared to let Mysterion vanish for good.
Until the day that Cartman suddenly ran up behind him and Stan at the bus stop in his stupid Coon costume and rasped "Stan Marsh, I've--"
"What the hell are you wearing, Cartman?" Stan cut him off.
Cartman's eyes narrowed, but amazingly for him he managed to keep his composure instead of rising to the bait. "I don't know who this Cartman is, but you must think he's a seriously awesome guy if you thought he could be me. Stan Marsh, I am The Coon and I've come to offer you an opportunity you won't want to pass up on; a place in the brand new superhero group Coon and Friends. As a founding member you'll get a whole .05% of the profit from any merchandise sells!"
"So, you're saying you want to play superheroes tonight?" Stan looked thoughtful for a minute, then asked, "Did you get Mysterion for your group?"
Kenny grinned under his hood as Cartman obviously snapped. "No, Stan, I did not get fucking Mysterion for my group! Mysterion's just a no-good quitter who gave up and went into hiding when the going got tough, which is part of why the Coon is a way better hero in every way!"
"Hey, man," Kenny protested, but went unnoticed.
"Do you really think you'll find anyone who wants to be part of a superhero group without Mysterion in it, Cartman?"
"God dammit, fine!" Cartman whirled towards Kenny, who he'd been completely ignoring until then, his hands curved like he wanted to claw him in the face, but he spat out, "Kenny, do you want to be a member of Coon and Friends?"
Kenny shrugged, but couldn't help noticing Stan was staring at him like he'd just done something amazing.