The first one they caught by surprise-stabbed him in the back of the head. Dean and Crowley had teleported themselves into the car that the Leviathans disguised as Sam and Dean had been driving. The Leviathan Dean was driving, and this is the one that Dean stabbed. He slumped onto the steering wheel, causing the car to veer off the road, landing upside down in a ditch. Black goo dripped from the back of its head, until the goo pooled on the roof of the car.
Crowley nodded and hummed his approval.
The remaining Leviathan spun around and stared at Dean. It shifted its gaze to Crowley, then back to Dean. In those few moments, it looked scared; and why wouldn't it? It had just witnessed its brethren killed—a feat which should be impossible. Its fear didn't last long, though, and it grinned maliciously. "Ah, Castiel's little pets. Come to avenge your master, I see?"
"Fuck you," Dean growled.
The Leviathan laughed—Sam's laugh. That just made Dean angrier. "I'm going to kill you," Dean whispered. "And you know I can."
"So does every one of us. And now we're all going to be hunting you down. That is, if I don't kill you first."
"Hey, I've been trying, but if you find a way, I'd love to hear it," Dean drawled.
The Leviathan and Dean both climbed out of the car. Crowley climbed out too and pulled his cell phone out, to film the two of them.
The Leviathan cracked its knuckles and punched Dean in the face. The force of it sent Dean stumbling back; he heard bone crack. The Leviathan punched Dean over and over. "I like my meat well tenderized," it explained.
"Well, in that case—" Dean's fist connected with its face. It hardly seemed to have felt it. Dean slammed his foot into the Leviathan's solar plexus. He was pleased to hear it gasp for breath and to see it stumble back and fall flat on its back. Dean pulled a bottle of borax from where it was concealed within his jacket. He grabbed a fistful of its hair and splashed the borax in its face.
"You know why this burns, don't you? It's because you're so filthy; you're a dirty, unholy oil stain," Dean said in a low tone. "That's why God locked you away, you filthy son of a bitch."
"It's a curious thing that you haven't been locked away by that logic."
"I am a storm door, holding back a much, much worse storm." Dean conveniently left out the fact that he was no longer holding back that storm.
Dean let go of the Leviathan, standing and kicking its face and gut. He scooped up the First Blade from where he'd dropped it. He'd yet to turn back to the Leviathan before he felt a knife stick into his neck. The Leviathan plunged the knife into Dean's windpipe. Dean whirled around and stabbed it in the back. It died almost instantly. Dean pulled the knife from his throat and fell to the ground, legs unable to hold his weight up.
Crowley ventured over, pointing the camera at the leaking Leviathan, then at Dean.
"What—" Dean rasped.
Crowley understood what he'd been trying to ask: "Helping."
Dean died before he got the chance to ask exactly how Crowley was helping.
Crowley stopped filming. He brought up the Washington Post homepage, and tapped their contact information page. He sent them an email with the video of "Sam and Dean Winchester's" deaths.
He slipped his phone back into his pocket and inspected the corpse that laid at his feet. "So much for being eternal," Crowley lamented. He picked up the First Blade, wiped the goo off with a hanky, and disappeared with a click of his fingers.
AHHHH OH NO GUYS DEAN'S DEAD WHO AM I GONNA WRITE ABOUT NEXT?!
Hahaha just kidding he's not actually dead, he just hasn't respawned yet, that's all!