Facing Hrívemir's sudden turn of rage, Sylas reacted instantly.
With a crack of displaced air, he vanished, and reappeared atop the dragon's back.
"Avada Kedavra!"
A brilliant flash of green light struck the Frost Dragon's spine. Hrívemir's immense body jerked, his muscles locking, and then he loosed a roar that shook the frozen sky.
"Damn it," Sylas muttered, teeth clenched, before vanishing again.
The Killing Curse had hit, but not killed. An ancient being born of Morgoth's forges, Hrívemir's soul was forged of the same darkness that had once defied the Valar. His spirit did not yield so easily. The spell tore at his essence, but did not unmake it.
And now, enraged beyond reason, the Frost Dragon's wrath erupted.
"Wizard!" he thundered, voice echoing across leagues. "I will see you die!"
His maw opened, spewing torrents of white death. Frost rolled across the land, freezing earth, stone, and air alike.
Sylas flickered through space again and again, Apparating between flashes of cold. Each time he appeared, it was only to vanish once more, drawing the dragon's fury away from Isengard, step by step.
Smaug soon joined the fray, his wings cutting through the air in a scarlet blaze. Though dwarfed by Hrívemir's colossal form, Smaug's flight gave him the advantage. He weaved through the clouds, spitting gouts of flame that sizzled against the Frost Dragon's hide.
Thorondor, the Giant Eagle, dove from above, swift as a stormbolt. He tore through the blizzard winds, evading icy breath, then raked his massive talons across a cracked plate of scales, ripping free a swath of flesh.
Hrívemir bellowed, whipping his head around, but pain struck again, this time from below.
His tail shuddered violently, Cerberus had sunk his three sets of fangs into it. The Three-Headed hound's venom hissed and smoked against the dragon's flesh, eating through even Hrívemir's icy armor.
Snarling, the Frost Dragon flung his tail with monstrous force. Cerberus flew like a stone from a catapult, crashing into a distant cliffside with a sickening crunch. His body hit the rock and slid limply to the ground.
"Cerberus!" Sylas's voice rang out, sharp with alarm. The hound did not rise.
The wizard's eyes went cold.
Black mist began to rise around him, swirling like a storm given form. His pupils bled away into white, and the air trembled with raw pressure as his body dissolved into a roiling sea of darkness.
In an instant, the Obscurus returned.
The black mist surged across the battlefield faster than the eye could follow. It struck Hrívemir like a living tempest, tearing at his scales and flesh, grinding the ancient dragon down grain by grain.
But Hrívemir was no mere beast. Snarling, he exhaled another storm, not outward this time, but inward. A spiral of cold air wrapped around his body, solidifying into glacial armor.
Layer upon layer of crystalline ice spread across his scales, forming an unbreakable carapace.
Smaug's flames washed over it in waves of molten gold, but could not breach it. Sylas's Obscurus form slashed and raged, yet only stripped away frost before the armor sealed again.
Hrívemir had become a walking glacier, untouchable, inexorable.
Then the dragon's gaze drifted past Sylas, down toward the men gathered near Orthanc. His lip curled in cruel amusement.
"You care for these insects so much?" he rumbled, voice thick with malice. "Then watch them freeze!"
Before Sylas could answer, Hrívemir reared back and unleashed a storm of cold upon the plains.
The temperature plunged. Frost rolled outward in every direction, swallowing the world in seconds. Breath turned to shards of ice in the air; the ground itself cracked beneath the spreading permafrost.
The cold deepened into a killing chill. Within minutes, the breath of every soldier and beast began to crystallize in the air; if the frost were not stopped, all life around Isengard would be sealed in ice.
Sylas's half-corporeal form surged forward through the storm. His upper body solidified from shadow into flesh, and with a sweep of his arm, he summoned living fire.
Fiendfyre.
The infernal blaze roared to life, rising around Isengard in serpentine walls. It formed a blazing barrier of protection, an incandescent ring that fought back the encroaching cold.
Then the fire shifted.
From the heart of the inferno, Sylas's body flared crimson and black, reshaping itself into a towering Fiendfyre Balrog. Chains of fire coiled around his arms; in one hand, he drew a whip of molten hatred and cracked it toward Hrívemir.
The lash struck true. The whip snapped across the dragon's glacial armor, fracturing the crystalline shell and exposing slivers of pale flesh beneath.
But Hrívemir was no ordinary foe. Snarling, he exhaled torrents of frost, freezing the Fiendfyre whip mid-swing. The infernal flame hissed, sputtered, and turned brittle under the absolute cold.
Fire and ice clashed without end.
Heat boiled the snow into mist; frost reclaimed it, turning it once again into drifting crystals. Soon, the entire plain was wrapped in a veil of steam so thick that sight itself failed.
In that mist, unseen wings moved.
The Basilisk Herpo slithered silently through the haze, circling behind the Frost Dragon. In a blur, he struck, his fangs sank deep into an unscaled patch of hide and pumped every drop of venom into the dragon's veins.
Hrívemir's roar split the heavens. He turned, jaws opening to obliterate the snake with an arctic blast, and met two burning orange-yellow eyes.
The Basilisk's gaze struck like a dagger of soul-fire. Hrívemir's cry became a shriek; his spirit shuddered as unseen wounds tore through it.
"Avada Kedavra!"
Sylas reappeared at the dragon's flank, wand raised. The green flash struck full on. The curse and the gaze together ripped through the ancient dragon's spirit; his roars faltered, his massive frame shuddered.
For the first time in millennia, Hrívemir felt fear.
Surrounded, by Sylas, Smaug, Thorondor, Herpo, and the blazing Balrog form, and with ten thousand warriors of Dunland and Rohan watching from below, he knew death had come within reach.
The Frost Dragon let out a final, furious bellow, unleashing a wave of cold to drive back his attackers. Then, in one desperate surge, he turned and fled.
The great dragon's broken wing dragged at his pace, but his limbs thundered across the plain. He ran northward, toward the jagged silhouettes of the Misty Mountains. He knew the southern and western lands belonged to men, Gondor, Rohan, Enedwaith, but the north promised concealment. There, amid shadowed peaks, he could vanish, heal, and one day return.
"After him!" Sylas shouted. "Do not let him escape!"
His body dissolved once more into smoke and storm. The Obscurus form ignited, black energy billowing like a living tempest.
It wasn't that Sylas was unwilling to let the Frost Dragon go, but he had heard the Frost Dragon's thoughts and knew this was a Dragon with an extremely strong desire for revenge.
The Frost Dragon already considered him an enemy, just waiting for an opportunity to retaliate in the future. Sylas always preferred to prevent trouble before it arose, so he naturally couldn't sit by and allow a Dragon that could emerge at any time to seek revenge against him to exist.
Sylas flew by his own power for the first time; in his Obscurus form, he seemed to have no weight or form, essentially being a mass of destructive magic. His flight speed was also very fast, directly catching up to the fleeing Frost Dragon.
The Frost Dragon wheeled suddenly, releasing another torrent of glacial breath.
Sylas, in his Obscurus form, dissolved into mist and shadow, letting the freezing blast pass harmlessly through him. The black vapor then surged forward like a living storm, wrapping around Hrívemir's colossal frame. The darkness clung to him like a sentient shroud, gnawing away at scale and sinew alike, corroding his body with pure destruction.
Hrívemir roared in pain, and once again turned his own cold against himself. He unleashed another wave of frost, sealing his body in layers of ice until he looked like a mountain of crystal. He sought not only to shield himself, but to freeze the black mist that devoured him.
Even Sylas dared not clash directly with that apocalyptic cold. His shadowed form scattered and then coalesced again at a distance, circling warily.
At that moment, Smaug and the Giant Eagle Thorondor swooped in from above, with Heilbo the Basilisk coiled around Smaug's neck like a living weapon.
Smaug's jaws opened, belching a column of golden-red flame that roared down upon the Frost Dragon below. Heilbo's slit eyes glowed fiercely, releasing his deadly gaze in tandem.
Hrívemir exhaled cold to counter the flames, but the moment he turned, his eyes met the Basilisk's.
His soul shuddered. The deadly sight tore through his spirit like a knife. His breath faltered for an instant, just long enough for Smaug's flame to strike his exposed side. The ice armor melted in torrents of steam.
Then Thorondor dove. His talons, large as ballistae, ripped through the shattered scales, tearing away a great strip of flesh and blood.
Hrívemir's scream shook the mountains.
"Avada Kedavra!"
The Killing Curse struck true. The Frost Dragon's immense body trembled, and the light within its soul guttered like a dying ember.
Its breath came ragged, its scales dulled, and its eyes burned with pure, manic hatred.
"You wish for my death?" the Frost Dragon bellowed. "Then let us all perish together!"
An overwhelming chill surged from his body. His throat rumbled with a low, resonant hum that made the air itself vibrate, ancient Dragon Magic, drawing on life essence as fuel.
Smaug's expression changed at once. "Not good! Master, he's burning his own life force! Fall back, quickly!"
Sylas did not hesitate. The black mist that was his body whirled away from the Frost Dragon like a receding tide.
A heartbeat later, the world froze.
The Frost Dragon detonated his cold. A wave of deathly frost erupted outward, freezing everything it touched, trees, rivers, stone, even the air itself solidified into glassy shards.
Within moments, more than ten miles of land lay buried beneath ice.
The shockwave struck Smaug and Thorondor even as they fled. Though they escaped the heart of the storm, frost crept over their wings and scales. Heilbo coiled tighter, his serpentine body sluggish and pale, nearly falling into hibernation under the chill.
At the epicenter of the frozen wasteland stood Hrívemir, half-buried in his own creation. He did not die, but he had sacrificed part of his life force to unleash this destruction.
Had he truly chosen to perish, the cold unleashed would have frozen even time itself.
Now, weak and faltering, Hrívemir could no longer breathe frost. Without another glance, the ancient dragon turned and fled deeper into the Misty Mountains.