Anyway, here's what I think Loki's backstory for the film should be. It's a blend of the comics, the myths, and one or two ideas of my own:
Loki was the son of the Giantess Laufey and her husband Farbauti. Loki was the runt of the litter, only about the size of a normal human or Aesir baby. Because of this, Laufey kept her son hidden from the rest of the Jotun. During one of the many wars between Jotunheim and Asgard, Odin slew Laufey and Farbauti in personal combat. He then found Loki hidden in their palace's nursury, and, wishing to honor two worthy adversairies who died honorably, took the child in as his own. Loki was raised with Odin's two other children, Thor and Balder. As Loki, who was still physically bellow average by Asgardian standards, was harrassed by others in his youth, Odin preformed a blood pact with Loki. The two were bound by blood in a way deeper than even family. None could willingly bring harm to or allow harm to come to the other. As such, the physical abuse ceased, although the psychological abuse continued.
As Loki grew, he found a way to get respect and get back at those who tormented him: He became a trickster. He would grift and prank all across Asgard, becoming a source of a musement and a target for scorn for many. However, up until this point, his mischief was just that. Mischief. Annoying, yes, but mostly harmless, and rather funny from an outside perspective. Eventually, he met and married the giantess Angraboda, with whome he fathered three children: Hela, Fenris, and Jormungandr. Due to Loki's very unique nature, his children were born mutated. Half of Hela's body was compleyely nrecrocized, Fenrir was a wolf pup, and Jormungandr was a very large snake. However, Loki loved his freak children just as any true father would.
Soon, it was proficiesed that Loki's children would grow up to become major threats to Asgard, and Loki could possibly betray them to their enemies. To take measures against this, Odin exiled Loki's children to the four corners of the nine worlds. Fenrir was chained to the ground, Jormungandr was banished into the seas of Midgard, and Hela was trapped in Hel, the land of the dishonored dead, and was forced to become it's keeper. Loki was outraged at Odin, but Odin felt that what was done had to be done, and that Loki was lucky that Odin trusted him enough not to banish him aswell. However, because of the profecy, Loki was made even more of a social pariah. Because of their children's exile, Angradoda commited suicide soon after.
Eventually, Loki remarried to the godess Sigyn, who bore him two very normal sons, Narfi and Vali. And though Loki apeared happy on the outside, inside his rage and grief ate him alive. Some years later, when Narfi and Vali were in their teens, it was proficiesed that Balder's death would ste into motion a series of events that would lead to Ragnarok, the twilight of the gods. Odin's wife shrouded Balder in countless protection spells, making him imune to all forms of violent death imaginable, to prevent this. However, Loki discovered that there was one chink in Balder's armor: Mistletoe was completely ignored when the spells were cast. In other words, if a weapon could be made from mistletoe, it could kill Balder.
Loki, acting upon years of hatred built up within him, fasioned an arrowhead from mistletoe and used it to kill Balder, who, ironically, was one of the few people in Asgard who treated him with any respect. Loki was soon captured by Odin. Because of their blood pact, Odin could not exicute Loki, However, since Loki's crimes could not go without being punished as harshly as possible, his death setnence was then placed upon his sons. Odin turned Vali into a rabid dog, who then ripped out his brother's throat, killing him. Vali soon succumed to his illness and died aswell. Loki was chanied to a rock under the earth with Narfi's intestines, with a snake's venom constantly dripping into his eyes. As Odin locked him away, Loki swore furthur revenge.
Recently, Loki escaped his prison, and was finally able to free his children from their exile. Their plan is to kill the now human Thor, and then lead an army of giants, dark elves, fire spirits, and the undead into Asgard and burn it to the grownd.
So, we have Loki as the mastermind, and Fenris, Jormungandr, and Hela's undead minions supplying the physical threats for Thor.
