In which Dean turns out to be the archangel Michael (surprise!) and decides that they're doing this Apocalypse thing his way (i.e. not at all), the rest of Team Free Will (plus Gabriel) help out, and the Host, the demons, and various other characters are along for the ride (eg. fellow archangels, grumpy hunters, hapless prophets, etc). Alternate universe.

Her name isn’t really Darcy, of course: her true name is something much older and a damn lot more powerful. Norse gods weren't the only supernatural beings in New Mexico when Thor was there.

“Eternity is really rather boring, John. Mortal life seemed as though it would be far more interesting.” Sherlock is actually the Devil, but he decided to live as a mortal because ruling Hell was boring.

When Loki attempts to mind-control Tony Stark in the middle of the Chitauri invasion, he unlocks powerful memories and abilities, and Tony realises that he's something greater and more powerful than he ever knew. And so is Steve Rogers, but that's a slightly different problem.