all the fic I wanted to write but didn't

The rings of the four horsemen don't work (rewatch before writing), Lucifer kills Michael, and they don't get rid of Lucifer. He's the version from the alternate universe, perfect suit over his Sam suit.

He locks Dean in a cage (which looks, for all intents and purposes, like the inside of a motel room). Reason for keeping him as yet unknown.

Dean believes Sammy is gone, so he attempts suicide. Over and over again, because for some reason Lucifer wants him alive and keeps bringing him back. It's a motel room, so all Dean's weapons are available. However, it's still a construct, so angel spells and shit don't work. If Dean has an angel blade, that doesn't work either. Or maybe they just don't work because Lucifer is no ordinary angel.

Lucifer doesn't want Dean to keep killing himself (for some reason), so he offers Dean the chance to visit with Sammy. Claims Sam is still in him, asleep, but he'll let him out for short periods. He doesn't want Dean to lose hope.

Dean's dubious, but soon believes that it's Sammy he's talking to. He gets a half hour at first, and they do the exposition thing (this is probably the first scene of the fic), and while he thinks they're screwed, still, every time he gets to see Sammy, Sam gives him hope.

They come up with a plan (fuck knows what I'm going to do here, but it's got to have plot), but also, they get fleshy with each other (Sam instigated).

The end, the twist, is that the plan doesn't work, because it's been Lucifer driving it all along. He's all, sigh, "Dean, Dean, Dean. You really thought it was Sam all this time?" and it turns out that Dean's been fucking (or rather, been fucked by) Lucifer all this time.