A/N: Listening to this song just reminds me of how utterly bonkers Leviathan Cas was. This ends with Leviathan Cas going to drown himself in the public river. There is a Cas fanvid with this song on Youtube. The song is Madhatter by Melanie Martinez.
'My friends don't walk, they run
Skinny dip in rabbit holes for fun
Popping, popping balloons with guns, getting high of helium
We paint white roses red,
Each shade from a different persons head
This dream, dream is a killer,
Getting drunk with a blue caterpillar.
I'm nuts, baby, I'm mad,
The craziest friend that you've ever had
You think I'm psycho, you think I'm gone
Tell the psychiatrist something is wrong
Over the bend, entirely bonkers
You like me best when I'm off my rocker
Tell you a secret, I'm not alarmed
So what if I'm crazy? The best people are.'
"This is going to be so much fun." Cas, no, the Leviathans, tilted their head, grinning manically. Bobby sat up, and crawled over to Dean. "Won't you play our game, friend?" Leviathan Cas crouched down to look into Dean's eyes. Dean recoiled, feeling Bobby at the side of him. He looked desperately at the doorway, but Cas caught his line of sight and tutted. "Tsk, tsk, no, no getting away this time Dean." The hunter was grabbed roughly by the shoulder and flung into the opposite wall.
Dean coughed up blood immediately, and raised his bruised face to look at Cas. "Cas," he pleaded. "Please Cas, please stop this. This isn't you. Come back."
"Cas is gone." The thing hissed. "He isn't here to protect you anymore." It smiled as it dumped an unconscious Bobby on the floor and stalked towards Dean. "You're my toy now." Dean choked, and felt one of it's hands clutch his collar. "You're crazy." The thing's grin widened. "We know." It started to punch and kick him until Dean was pretty sure he had at least two broken ribs. "Dean?" Shit, Sam! The thing's head turned to Sam's voice, and it gave Dean a shit-eating grin. "No!" It clamped a hand over his mouth. It's palm was cold and clammy, and it had a line of black goo dribbling down it. "We're in here Sam." It called in a Cas-like voice. It winked at Dean, then turned to face the doorway.
Sam appeared, and Dean struggled, but the Leviathans kept him were he was. "Cas, where's Dean?" It was then that the younger Winchester noticed Bobby's unconscious form. He looked back with wide eyes. "You're not Cas, are you?" The creature laughed and grabbed Dean by the neck and swung him around so that Sam could see him. "Point one to Sammy dear." It laughed again, a high pitched tinkling sound, and Dean really wanted to cover his ears. "Sammy run!" He shouted.
"Not so fast." Cas said, and with a flick of his hand Sam was on the floor in front of him too.
The thing preceded to let go of Dean and fling his brother across the room. When Sam tried to get up, it walked to him and began to give the same violent beating it had given Dean earlier. Dean took the opportunity and grabbed his gun. He pointed it at the things back and shot. Cas - no, not Cas, not anymore, he reminded himself - the creature, jerked slightly with each shot, bit otherwise paid it no mind. Dean emptied a whole click, but it did nothing. Funnily enough, when he stopped shooting, it turned back. It looked worse, black goo dripping everywhere, coming from it's head and hands. "Not looking to good there." Dean commented as it shuffled towards him. "I reckon your vessel's giving in. You're going to explode." It smiled then, this time, it looked cold and detached, the sort of grin a crazed druggie with a gun would give you before he shot you. "I am," it whispered sweetly. Dean saw Bobby and Sam both sit up and cower together. At least they were awake. He turned his attention back to the creature. It was now face to face with him, only an inch of space between them. "But I'll tell you a secret." It leaned closer, it's lips just brushing Dean's ear. He shivered, goosebumps raising. "I know which way to go." With that, it stood straight and shuffled off, out of the doorway and down to the entrance. Dean looked to Sam and Bobby. "We have to follow them." he said.