15 Comic Book Movie Deaths That Didn't Last
9. Loki - Thor 2
Cause Of Death: A surprising bout of selflessness.
Having been tempted into service by Thor's promise that he can kill Malekith in vengeance for the murder of the unfortunately named Frigga, Loki forms an uneasy alliance with his half-brother to take on the Dark Elf, tricking their enemy into believing that he has come to betray his kin.
Naturally, Loki's heroic turn can only spell one thing for him, and he is mortally wounded while battling the balrog like over-powered Algrim (possessed to become Kurse). He dies and Thor mourns him, proclaiming him a hero and vowing to tell their father of his sacrifice, which he doesn't need to do, since it turns out that Loki was just faking, and turns into his mysteriously absent father to offer Thor his throne.
Quite what he would have done if Thor had agreed remains to be seen.
The Science Behind The Revival
Who knows? The writing of The Dark World is so off at the end that Thor and his worldly girlfriend Jane just randomly find a portal in a cave, and there's literally no explanation of where Odin has gone, when he's replaced by his malevolent adopted son: so looking for meaning in Loki's recovery is probably folly. Let's just put it down to magic or something.