Loki's been a bad boy. In fact, he's been the big baddie for both last year's Thor and this summer's hit movie The Avengers. Heck, he's been so bad (in a good way) that he's even returning for an another encore in Thor: The Dark World. But will Loki make another return to be a pain in the butt for Earth's Mightiest Heroes in The Avengers 2?