During the episode "The End," Dean Winchester sees the future. It's one that Lucifer's influence is all over.
Added:
Why is Dean on the run? Because the future he's a part of during the episode "The End" is downright scary.
Added:
Armed, Dean takes to the street in this scene from "The End." This is a key episode, as the character gets a glimpse of an awful future.
Added:
What the Hell?!? Dean is thinking that, literally, during the episode titled "The End." He gets a glimpse of what Lucifer has done in the future.
Added:
Dean goes into the future on the episode "The End." He doesn't like what he sees.
Added:
Dean travels to the future on the episode "The End." He doesn't find anything that gives him hope.
Added:

Supernatural Season 5 Episode 4 Quotes

Future Dean: Okay. If you're me... then tell me something only I would know.
Dean: Rhonda Hurley. We were, uh... 19. She made us try on her panties. They were pink. And satiny. And you know what? We kind of liked it.
Future Dean: Touché.

Dean: You know, it's kind of funny, talking to a messenger of God on a cell phone. It's, you know, like watching a Hell's Angel ride a moped.
Castiel: This isn't funny. Dean. The voice says I'm almost out of minutes.