I'm sure this has probably been done just short of a billion times - on this website alone. But I just couldn't resist the temptation of spewing out my own.
It can't be certain what exactly
caused this mess, but I'd hazard a wager that it's Mordecai and Rigby's fault. Seems they went dabbling into the supernatural again and somehow
managed to drag Finn, Jake and all their friends along for the ride as well.