The colossus moved faster than anything that size had any right to, one massive, fused arm sweeping low across the chamber floor in a blow that would have ended the fight early if Stephan hadn't thrown himself sideways into a roll, coming up already swinging Ember in a bright arc across the nearest exposed joint.
It didn't even slow down.
Xavier answered with a bolt of concentrated flame aimed at the same joint, meant to soften the bone before Stephan's next strike... and watched it fizzle out early, guttering into nothing a few feet short of its target, dissipating like a candle in the wind.
"...That's new," he muttered, already drawing on more, frustration mounting as a second attempt curved wide and scorched a harmless line across the stone floor instead.
"A LITTLE HELP WOULD BE GREAT," Stephan shouted, ducking under a second swing and answering with a flurry of quick strikes along the colossus's leg that chipped bone but didn't seem to meaningfully slow the thing down.
Xavier tried again, and again, and each attempt came out just slightly wrong — a beat too slow, an angle too shallow, power that should have been there simply not answering the way it usually did. Whether it was exhaustion from a sleepless night, the psychological weight of Bruce still missing somewhere in the dark, or something about the vault itself dulling his focus, nothing about tonight was cooperating with him the way magic usually did.
"Go for the head instead of the joints!" he called, backing up as the colossus rounded on him instead, evidently deciding the one who kept missing was still worth investigating.
"I'm A LITTLE BUSY-" Stephan's protest cut off as he was forced into a full sprint, dodging a swipe that took a chunk out of the floor where he'd been standing a half-second earlier.
The fight became, for a stretch neither of them would remember fondly afterward, mostly a matter of survival rather than strategy. Xavier's spells consistently underperformed just enough to be useless without being harmless, forcing him to fall back on his blade instead, trading actual sword strikes against a monster three times his size while Stephan absorbed hit after hit that would have flattened almost anyone else, armor and stubbornness apparently the only things keeping him upright.
Xavier darted in low, sword catching a thin seam between two fused ribcages, and for half a heartbeat thought he'd finally found real purchase.
Until the colossus twisted with a speed that shouldn't have belonged to something so enormous and flung him bodily across the chamber.
He hit the floor hard, rolled twice, and came up already reaching for his blade again before his body had properly finished registering the impact.
"Xavier!" Stephan's voice cracked with something closer to panic than his usual bravado.
"I'm fine, I'm FINE!" He wasn't entirely sure that was true, but there wasn't time to check. He forced himself back into the fight on instinct, sword raised, and tried once more for fire — a focused lance of it this time, aimed at the thing's cobbled-together skull instead of a joint, in case a different target broke whatever streak he was on.
It didn't. The flame guttered a body-length short again, thin and apologetic, and the colossus didn't so much as flinch.
"Okay," he said out loud, mostly to himself, teeth gritted. "Okay. Whatever. Sword it is. Again."
He threw himself back into the melee, matching Stephan's rhythm as best he could — one of them drawing an arm's attention while the other carved at whatever joint was left exposed. It was a clumsy, improvised partnership built entirely out of adrenaline and the simple refusal to lose. It wasn't elegant. Twice Xavier felt the wind of a fist pass close enough to ruffle his hair.
Once he barely got his blade up in time to keep a downward blow from splitting him in half, the impact numbing his whole arm to the shoulder and sending him staggering back several full steps.
"You're doing better than me right now," Xavier admitted, breathless, parrying a stray swipe that nearly took his arm off at the shoulder.
"I am absolutely not..." Stephan gasped, blood trickling from a cut above one eyebrow, "...doing better than you right now. I am doing WORSE. I just haven't fallen down yet-"
The colossus reared back for a strike that both of them could see coming from a mile away, and neither of them had the position to actually avoid. Its whole fused, monstrous bulk rose to bring both massive arms down at once in a blow clearly meant to end things. Xavier tried, one last desperate time, for something — anything — and this time the fire answered, imperfect and smaller than he wanted, but real, catching along Ember's blade the instant Stephan swung it up to meet the falling arms.
It wasn't enough to stop the blow outright. It was enough to turn it, redirecting one massive fist just wide of Stephan's skull and into the stone floor instead, the impact shaking the whole chamber and sending both of them sprawling from the shockwave. Stephan rolled with it, came up scraped and gasping, and drove Ember two-handed straight into the crack his own deflected blow had opened in the colossus's chest.
The whole towering mass shuddered, groaned, and collapsed all at once into a scattered, lifeless heap of ordinary bone, the strange, unified purpose that had held it together finally, completely gone.
For a long moment, neither of them moved.
"...We did it," Stephan said, flat on his back, staring at the ceiling.
"You did it," Xavier corrected, dragging himself upright and offering a hand down. "I mostly stood there missing things."
"You helped at the end. That counts." Stephan took the hand, wincing his way back to his feet, the cut above his eyebrow still trickling blood he didn't seem to have noticed yet. "Everyone's allowed one bad night. Even you."
Xavier managed a tired, grateful laugh, and didn't argue the point, mostly because arguing would have required more energy than he currently had left in his entire body. He looked down at his own hands, still faintly warm from the one spell that had actually worked, and turned them over slowly, as if the answer to what had gone wrong tonight might be written somewhere on his own palms. It wasn't. Some nights, apparently, the fire just didn't want to cooperate, and there wasn't a lesson in that beyond the obvious one — that Stephan had carried more than his fair share, and that Xavier owed him for it.
"Next one's on me," he said quietly, mostly meaning it as a joke, and only realizing after he'd said it that he meant it seriously too.
"Damn right it is," Stephan said, clapping him on the shoulder hard enough to make him wince, already scanning the scattered bones around them with the particular restlessness of someone who hadn't forgotten, even for a second, that this still wasn't over. "Now let's go find Bruce before I have time to feel any of... this."