"Move away, please"
Loki turned away from his brother's anguished face to look at the Midgardian who'd spoken. There was nothing distinctive about the man. He had short-cropped hair, receding slightly in front, a clean-shaven face, and the slight build which was typical of mortals. He was even garbed in the ubiquitious "suit" common to this realm. He was in all ways unremarkable, and Loki would have completely disregarded him if it weren't for the rather large gunlike weapon he was carrying, its muzzle pointed directly at Loki.
Not being familiar with the device in question, Loki elected to slowly straighten and move away from the control panel of the "Hulk cage", keeping his eyes on the new combatant. Then he created an illusion of himself, spelled to continue moving in a non-threatening way, leaving his real self-- safely shrouded in invisibility-- free to stalk this new combatant unseen.
"You like this?" asked the human in a mild, almost-conversational tone as he started walking forward. Despite his overall forgettability, there seemed to be something naggingly familiar about him. "It's a 0-8-4 we found at a spaceship crash site." With a slight shrug, he added, "Even I don't know what it does." He tapped a button on the device, resulting in a sinister hum and a reddish glow at its front end. "Wanna find out?"
By now, Loki had completely flanked his adversary. No, I do not he thought as he stabbed the sharpened end of the scepter into the man's back, inflicting a wound which should be severe enough to keep him out of action until affairs were concluded.
"NO!" screamed Thor, thumping his fist against the transparent wall of Loki's erstwhile cell. Loki idly wondered if this was one of Thor's mortal friends as he allowed his no-longer-needed simulacrum to dissipate. The strength of his brother's reaction seemed to indicate thus. If so, Loki hoped he survived; unfortunately Thanos's compulsions didn't allow him the freedom to waste energy on actions which didn't contribute to bringing about his desired victory, and healing an active foe didn't qualify.
Not outright killing Thor himself was going to tax Loki's considerable ingenuity enough. He forced himself to concentrate on Nick Fury's smug explanation of how the Hulk cage worked as he walked back toward the controls. He had to keep the expected lethality of this action in mind to satisfy the geas he was acting under.
So he threw himself completely into his role as he sauntered back to face Thor. He even gestured to the scepter's blade as if to say See? I can be a real warrior like you. Then he turned and stepped back to the cell's controls, listening to Thor's tortured breathing as he flipped open the little door over the drop controls. He turned his head to meet Thor's betrayed eyes as he flicked the control which opened the aperture in the helicarrier's deck.
Then he extended a slightly-trembling hand to hover over the button which would release the cage to tumble to earth. The part of him resisting the mad Titan's rule desperately told himself that Thor WOULD survive the drop, of course he would, he was Thor, the strongest and toughest of the Aesir. This litany was less than reassuring, especially since he had to simultaneously insist to his enslaved self that Thor's death was assured.
This internal conflict was interrupted when the forgotten human spoke up again, saying "You're going to lose."
Loki turned to look at him, intrigued-- and grateful for the interruption. "Am I?"
"It's in your nature."
Since Loki was in fact doing everything he could within the constraints placed on him to sabotage himself, this comment should not have rankled. It stung nonetheless, bringing back memories of all the centuries of Aesir mockery he'd endured for using "trickery" instead of "honest battle".
"Your heroes are scattered," he pointed out, walking back toward the fallen man. "Your floating fortress falls from the sky. Where is my disadvantage?"
"You lack conviction."
Annoyed, Loki retorted "I don't think I..."
That was when the mortal fired the scavenged weapon at him. Loki's last thought was that his mother had been right: His curiosity had proven to be the death of him.
Thor watched Loki turn and start responding to Coulson's words with a stirring of hope ... and not just because Loki was no longer poised to drop him out of the sky. Perhaps Coulson's calm logic and wry wit could get through to his wayward little brother when Thor himself couldn't. Please, Loki, stop; you know this is madness. You were always the one to urge caution and reason-- has your jealousy changed...
Thor's hopes were shattered when weapon's beam struck Loki's midsection and lifted him off his feet, then enveloped him in a sphere of coruscating colors. Truly, he could not blame Coulson, for it was his duty to defend his realm, and Loki had brought this down on his own head by his actions. He could only pray to the Norns than Loki was left alive by the strange device.
The effects looked like no weapon Thor had ever encountered before. He could sense some kind of seidr, singing faintly on the very edges of Mjolnir's range. The "feel" reminded him of multiple cables snapping under high tension.
Then the forcefield vanished and Loki's limp body dropped like a stone to the deck. Thor's jaw dropped with shock when he saw what had befallen his brother. It was shocking enough to see Loki with blue skin and Jotun lines in his face, but what was truly astounding was how young that face looked now. Loki looked no more than 600 or 700 years old-- a mere boy on the cusp of puberty. It was hard to judge from this angle, but Loki seemed to have shrunk to the size he'd been at that time as well.
"So that's what it does," murmured Coulson.