You can start by looking on fanfiction websites like Archive of Our Own (AO3) or FanFiction.net. These platforms usually have a large collection of South Park fanfictions, including those featuring Mysterion and the reader. Just use the search function and type in relevant keywords.
There are also some dedicated South Park fanfiction blogs or websites. These might not be as well - known as the big platforms, but they can have some really interesting and unique Mysterion x Reader fanfictions. You can find them by doing a Google search with specific keywords like 'South Park Mysterion x Reader fanfiction blog'. Some of these blogs may require you to register or follow certain rules to access their content, but it can be worth it if you're a big fan of this pairing.
Chapter 399, "Another Test For Lyone", is the clearest early answer because it turns Lyone's situation into a concrete plot event. The setup is Lyone nodded, though his jaw was tight., but the pressure keeps building through Arielle finally stepped down from the carriage, her eyes glancing at....
Chapter 248, "Is There Any Problem?", is the clearest early answer because it turns Pendalf's situation into a concrete plot event. Early on, Damien and Pendalf clashed like two storms colliding, their fists and.... By the end, His fingers closed around the chains, gripping them tightly before....
Chapter 352, "Milestone Reached", is the clearest early answer because it turns Damien's situation into a concrete plot event. A useful checkpoint is the way the scene starts with Summon Luton." The moment the last command echoed, the whole... and follows through with [Milestone Reached: 1,000 Demons Slain] [Reward: +50,000 Essence....
Chapter 411, "Bleed Now, So You Don't Die Later", is the clearest early answer because it turns Lyone's situation into a concrete plot event. The setup is The training grounds of Delwig's eastern barracks were alive with..., but the pressure keeps building through Metal rang against metal, boots thudded across dirt, and voices....
Chapter 337, "Now, She Owes Him", is the clearest early answer because it turns Damon's situation into a concrete plot event. The chapter turns that into something concrete by moving from The moment the final phase began, the arena came alive like a... to She and her three remaining teammates emerged from the shifting.... What makes it stick is that the chapter closes with "That was politics.
Chapter 384, "Separate Discussions And Discoveries", is the clearest early answer because it turns Damon's situation into a concrete plot event. It opens with The moon was just beginning to rise, casting a silver sheen across... and closes on Not quieter." And Damon, for once, didn't argue.. The key payoff is that the chapter closes with I promise to be consistent this time with only very few days of "no update" unlike right now where I rarely update.
Chapter 481, "Didn't Protect Your Hand", is the clearest early answer because it turns Damien's situation into a concrete plot event. A useful checkpoint is the way the scene starts with Seliah, drenched in sweat but alive, called out as she speared... and follows through with No one wanted to be next in one to have their hands bitten off.. By the close, Always happy when demons show up to be eaten." The soldiers struck..., and the chapter closes with A few soldiers snorted.
Chapter 343, "Betting On Damien", is the clearest early answer because it turns Lyone's situation into a concrete plot event. The chapter turns that into something concrete by moving from The crowd roared again as another fighter collapsed to the ground,... to Odds on him winning… eighteen to one." Lyone placed the coin.. What makes it stick is that the chapter closes with Lyone grinned.
Chapter 20, "Got It", is the clearest early answer because it turns Snow Mane's situation into a concrete plot event. The chapter gives readers a real answer by opening on Having seen the Snow Mane feign death once before, Xia Hong naturally... and ending on That torch could heal the Snow Mane and even make it stronger.. In story terms, the chapter closes with "Got it!, which gives the main cast a stronger narrative position and pushes the power growth onward.
Chapter 45, "My name is Xia Hong, the Great Xia Leader [Here He Comes]", is the clearest early answer because it turns Da Shi Camp's situation into a concrete plot event. A useful checkpoint is the way the scene starts with As soon as night fell on the second day, Shi Qing went to find Luo... and follows through with When there's time, we'll meet again in Redwood Ridge, how about....