In retrospect, John ought to have seen it coming. You don't have an entire mental hospital taken over by demons as the site of a infernal-celestial battleground without drawing some attention. (Or, the Winchesters finally hit Los Angeles.) Multichapter. Slooow but alive, I promise.

The two Winchester boys have met other hunters before, but they never expected to meet the exorcist, John Constantine. Though they literally are doing the same thing, making them coping with one another is after all not an easy job…set in season 4

Castiel was chosen to insure the Boy-Who-Lived did his job. He never thought the killing curse would scramble his memories until he had no recollection of who he really was though. Now Cas Shields has to survive as a psychic who just happens to be a wizard while training with his 'big brother' Constantine. Can Cas remember who he once was? HP/Supernatural/Constantine cross

Betrayal can destroy anyone, in this case its going to destroy the World as a whole if its not prevented.

[ON HIATUS] While visiting Hell, John Constantine stumbles across a piece of evidence that leads him to the Winchesters' door with shocking news about an old friend... NOTE: this is long and rambling. I may take forever to update. Contains very light Destiel, FYI

All Dean Winchester wanted to do was find out what happened to his little brother. All Castiel wanted to do was find a way back to Heaven after his Fall. Who would have guessed things would end up like this? Supernatural/Constantine AU-crossover.

AU. “John Constantine, I am Castiel. I’ve been sent to return something to you.” Chastine. Dean, Castiel.

SupernaturalConstantine crossover. Sam, Dean, and Jo go to LA to consult with an exorcist and find themselves caught up in a battle that transcends heaven, earth, and hell.