The Coon, with the dark lord Cthulhu on his side, seeks revenge against Coon and Friends. Cartman has his friends all banished into oblivion, and it's up to Mysterion to kill himself and rescue them from the other side. He goes to the goth kids' house where he learns only an immortal can kill another immortal. Mysterion knows who must defeat Cthulhu.
Mysterion, along with Mint Berry Crunch (apparently Bradley Biggles, the little brother of the fat goth chick), head to face off with Cthulhu and Coon as they slaughter Justin Bieber and fans. A parody of Jor-El appears to speaks to what appears to be Mysterion, revealing him to be from another planet and the only person with the power to stop Cthulhu. However, in a fun twist, it turns out to be Mint Berry Crunch he was talking to.
Using the power of mint and berry, he defeats the Cthulhu, rescues all his friends, and plugs up the BP oil spill. Oh and they lock up the Coon with the other super villain, Professor Chaos.