A/N: You know, I have never had Loki in a story before this one. Now he's a constant character and Bruce is hardly even in them! This makes me sad. D: I need to write something with Bruce.
No one really knew where Jack Frost stood. He would show up at random times, generally in the middle of a fight. On the occasions when they weren't fighting Loki, he would always side with the Avengers, but when they were, it was a toss-up as to which side he would choose. There were times when he didn't pick a side, just stood away from the battle and watched. During those times, at least one person would feel the cold wetness of a snowball hit their back. Jack would just grin and blame someone else. He had actually stopped one fight when he did it to Loki and the trickster left to chase him down.
Because of this, they hadn't really seen him fight much. With Loki he never hurt anyone, mostly just froze things, and against any other opponent he tended to hang back and make sure no one got hurt. The team mostly just assumed that he wasn't a good fighter, that he didn't know how to. Of course, Loki scoffed at that, he had seen the teen fight many times, usually against himself. Loki knew what the spirit was capable of. He wasn't about to enlighten his brother's friends though. He wanted to enjoy their looks of shock when they saw Frost finally, really fight.
When major cloud cover moved in, turning the sky black, the Avengers almost didn't think anything of it. In fact, if it had happened at night, they probably wouldn't have. Even now it registered no more than a small comment. Until Loki materialized in their living room. Before they could go for their various weapons, he held up a hand.
"Spare me the pointless diatribe. As much as I am loathe to admit it, I'm afraid I need your help. Or rather, Jack Frost does." He said, looking rather pained.
"Jack? What is the matter?" Thor asked
"Why should we believe you?" Tony said at the same time. Thor all but glared at him in response.
"My brother does not lie about Jack Frost." He said simply. Tony threw up his hands and headed towards where he kept his suit.
"Well, sure, if it's Jack, then of course we'll go. Because maybe that's the one thing that the god of lies won't lie about." He muttered the whole way. Meanwhile, the rest of the team was ready to go, except for Bruce. He was sitting in what he had claimed as his armchair, drinking tea and looking rather peaceful. Loki raised an eyebrow at him.
"We may have need of the beast." He stated. Bruce sighed.
"Is there another alien army invading?" He questioned.
"The closest thing to it." Loki answered grimly.
Jack wasn't sure where the Nightmares had come from. He had noted the heavy cloud cover when he and Loki were hanging out in the latter's apartment. Well, if Jack perpetually bugging Loki could be called hanging out. He didn't think anything of it, until something shot by the bay of windows. Something that looked suspiciously like one of Pitch's creations. Jack had followed immediately, throwing open a window and jumping out to follow. Loki had yelled at him, something about being an idiot, and thinking for once. Loki had then followed him and helped fight. Jack was fairly certain that he'd seen the sorcerer send off a clone, probably to get reinforcements. He hoped they would be the Guardians: he wasn't certain if the Avengers would even see the Nightmares.
After leading them to the battle site, the Loki they were following shimmered out of existence. They noted that he was now-or had been-fighting a little ways away. The enemy appeared to be black horses made of sand, with golden eyes. The main problem appeared to be numbers, not necessarily strength. These observations took only seconds, then they saw Jack. He was bounding from roof to roof, a pack of the horses behind him. As they watched, he shot up into the air, the horses not far behind. Just as he was about to be engulfed, there was a bright light and a crack! The now iced horses fell to the street below, breaking into a million pieces.
"…did anyone else know he could fight like that?" Clint asked.
"No. He's been holding back…" Natasha answered, sounding slightly awed. Their conversation was interrupted by the arrival of the boy in question. He didn't even appear to be breathing hard.
"Hey. You guys see them?" He asked without preamble.
"Yeah, what exactly are they?" Tony asked.
"Nightmares. I'll explain more later, but for now just know that as long as you aren't frightened of them, they shouldn't attack you." He explained curtly, very unlike the Jack Frost they had gotten to know. Tony flipped down his faceplate.
"Right. Don't be afraid of the creepy-ass magic horses. Got it." With that they were off, although throughout the battle, they watched both Loki and Jack. Surprisingly, apart from a few glares, Loki showed no inclination towards attacking them. As for Jack, he was finally showing his full power, moving everywhere at once at once, blasting the Nightmares until a thin layer of ice coated everything. The battle seemed to last forever, but it was over in about fifteen minutes, with minimal injuries. After all, it is difficult for horses made of sand to harm them. Jack landed next to where the tired heroes were standing. He ran a hand through his hair, dislodging bits of ice.
"Well, that was fun, wasn't it?" He said cheerfully, appearing weary, but no more so than if he had sprinted around the block. The Avengers stared at him.
"You can fight." Tony said, sounding somewhat dazed. Jack shrugged, still grinning.
"Well, yeah. What, did you think the Guardians were called that for the fun of it?" He answered smartly.
"Indeed. And I would not associate with someone unable to defend himself." Loki's voice made more than one of them jump, but he merely stood near Jack, arms crossed and a smirk on his face.
"We have had many adventures together!" Thor boomed, clapping Jack's shoulder while beaming at Loki. The latter gave an even more mischievous smirk.
"In fact, Jack, do you remember that one time in the Alps when-" He was cut off by Jack's hand slapping over his mouth.
"We agreed never to speak of that time!" He exclaimed. Thor's laughter boomed through the now-quiet city while the rest of the team watched in something approaching awe. They had never seen this side of Loki, and could almost see why Jack considered him a friend. There was an awkward silence before Tony spoke up.
"So, who wants pizza? I'll order in and we watch Primeval. Dinosaurs and pepperoni is the best, really." He said brightly. Everyone agreed to this and moved off. Except for Loki, who remained rooted to the spot, Jack hovering in between. Tony glanced back at them.
"C'mon, Reindeer Games. I'm sure we can call a truce for one night." The invitation was all Jack needed to grab Loki's arm and drag him to the Tower. Surprisingly, the trickster god didn't complain all that much.