Author's Note: Well, this sounded a lot cooler in my head, but my secret (or not) tumblr crush Anyaa (longlivetheboyking) mentioned how there's no torture-y Samifer fics so I tried to write one and it's not quite Samifer but I TRIED OKAY?
"Dean told you about Alistair, sure. But who do you think Alistair learned it from?" Lucifer's words were punctuated by another flash of light, another scream as Sam felt his body tear open at the seams. He writhed and struggled, but really where was he trying to go? Where could Sam go, in this space-between-spaces, where he had dragged the devil kicking and screaming? He was a human, one trembling soul against the wrath of an angel.
"Do you think this will end, Sammy? You think that I'll get bored eventually, forget about you? You're the reason I'm locked back in this stinking cesspit of a cage again, and I'm not going anywhere." Lucifer picked Sam up by the neck and threw him, and when Sam landed he was in a different place entirely. The landscape of the cage was always changing, always being torn apart and remade, just like its inhabitants. Now Sam was lying naked on a flat stone, and Lucifer was Nick again, leaning over him with a leer.
"When I get tired of playing with you, that's when the fun is really going to start. You remember Lilith? My first and favorite? Since you killed her, it seems only fitting that you would be her replacement. So let me tell you exactly what I'm going to do." Lucifer straddled Sam, pinning his arms down with one hand when he tried to scramble away.
"I am going to torture you until you break, until you shatter. I will hurt you until the only thing you can say is my name, until the only thing you know is who I am." A knife appeared in his other hand and without any warning Lucifer drove it through Sam's right eye with superhuman force, pinning his head to the stone beneath it. Sam screamed and bucked, waiting for darkness to take him, but it wouldn't. Fully conscious, fully aware, he felt the shattered bone at the back of his skull dig into his head when he moved, felt each splintered nerve ending as Lucifer twisted the blade and tore it out, leaning his head down towards Sam. His breath turned Sam's cheek black with frostbite, and the hunter's blood froze on his skin.
"And when all that's left of you is a quivering shadow of a soul, I'm going to build you back up into something a thousand times more magnificent. Lilith will be like a child compared to you. We'll have so much time to work." To his horror, Sam felt Lucifer's forked tongue on his face, lapping up the blood, scraping painfully across his burns. "And Sam, if you don't come out just the way I want…" Lucifer's lips settled over the gory mess of Sam's eye, and he breathed the last words gently into his skull, freezing Sam's thoughts. "Then I'll have to do it over again." Sam felt the devil's lips curve into a smile against his face, and even though he knew no one could hear him, he screamed.