My little take on how I think the series might end. It's a two parter, I'll try to have the second part up soon.

Sam stood in one the edge of the abandoned warehouse, staring at the awful carnage before him. He knew, but still wondered, how the hell he ended up here, angels and demons dead at his feet. His brother also lay dead right behind him, killed by Sam himself and Sam knew that Castiel was not far away, dead by Dean's own hands. Everything had just gotten so far out of hand, Sam wanted to hang his head and cry.

Sam had honestly thought they had succeeded in saving Dean all those months ago, turned him back human after the Mark had made him a demon. Honestly, he should have seen the signs. They way Dean killed monsters with a little too much glee, the way he was willing to allow humans, innocent people, to be killed if they came close to getting in his way. But Sam had just pushed those doubts away, dismissing them as remnants of what Dean had gone through. The process of "curing" Dean had burned the Mark off him, but his soul apparently remained blackened by it.

It wasn't truly until about a week ago, when he noticed the telltale signs, ones he couldn't ignore anymore. The persistent scent of sulfur in the Bunker, or Dean's unexplained disappearances at night or worse yet; the sudden appearances somewhere when Sam could have sworn Dean had not been there a minute ago. One thing led to another and the next thing Sam knew, he was watching Dean lead an army of demons against humanity. And when angels stepped in, Dean had killed them in droves, too.

Castiel had thought he could get through to Dean and confronted him. The two had fought for a long time, neither tiring although from what small amount of the fight he saw, Sam could tell that it was killing Cas to have to fight his closest friend. Sam had been busy fighting off Dean's demons and had only gotten to them at the end of the fight, only minutes before Dean ran Cas through with his own blade. In the end, Dean had won. The explosion of white light seemed to do nothing to slow down or hinder Dean in any way.

The brother in Sam wanted to try reasoning with Dean, but knew it would be in vain. Their earlier conversations had not ended well, usually with Sam knocked unconscious and Dean gone by the time he awoke. Sam still remembered the last time he'd confronted his brother in the Bunker.

"Dean, just stop, this isn't you!" Sam pleaded, trying to stop his brother from leaving the Bunker in search of things to kill.

"Really? What do you think I've been training for my whole life, Sammy?" Dean sneered in reply. "Dad wanted a perfect little soldier, he never even realized he was creating the greatest leader demon-kind would ever know!"

"You know that isn't true Dean! Dad would be rolling over in his grave if he knew what you'd become." Sam had known it would be a low blow, but he had to try.

"Well, then it's a good thing Dad doesn't have a grave then, huh?" Dean said, throwing his fist out to connect with Sam's temple.

Instead of trying to reason, after watching Dean kill his friend, Sam turned and ran from the room. He was hoping to lead his brother straight into the devils trap painted at the end of the hallway. Dean had avoided it when the fighting started, instead sneaking in a back door and cornering Castiel in a storeroom. Luckily for Sam, Dean took the bait, following him and shouting threats and obscenities after him.

"You really think running will work this time Sam?" Dean had called, following close behind. "All you ever do is run away, why don't you turn around and fight me you whiny little bitch!"

So Sam did just that; after passing through the trap and getting a safe distance away, he turned and took a fighting stance. Dean charged forward, prepared to end Sam's life but was practically thrown backwards when he hit the edge of the trap. He had glared up at the paint on the ceiling.

"You really think a simple devils trap will hold me?" Dean growled; his eyes black, face and body covered with blood.

"You're not a Knight anymore Dean, you're just an average demon now." Sam said, pointing to the mangled scar on Dean's arm. "You can't break this one."

Sam stepped forward then, standing right at the edge. He looked into Dean's face, his own filled with sorrow for what he was about to do.

"I'm sorry it has to be this way, Dean" Sam said, pulling the demon knife from his back pocket. "But this has to stop, all of this."

"You think you're gonna kill me? Well, that's rich! You forget, I'm still me, Sam! I'm still Dean!" Dean yelled. "You think you can kill your own brother?"

Sam had flinched at that comment, remembering the first Dean had said it to him, on his back and in pain from the shotgun shell of rock salt to the chest Sam had shot him with.

"I'm sorry, Dean." Sam said, striding forward, prepared to give the final blow. Dean had fought him for a few minutes, but there's only so far a demon can go inside a trap and the fight didn't last long. Dean had gasped when the knife struck him in the stomach, lightening flashing in his veins as the demon side of him died, the human side gone long before.

Sam shuddered remembering how he had gotten here, so caught up in the memories of the last few hours that he never noticed the flutter of wings behind him. He jumped when he heard a voice from his past.

"Hiya Sammy!"

Which mystery characher do you think is gonna show up now?