I realized this yesterday and holy crap it's a doozy. In the season finale Death says that he can't remove the mark because it would break the seal and let the darkness free. And yet in episode 10-12 "About a Boy" Dean is turned into a teenager and the mark is gone. So the darkness should've been released when the witch's spell was cast on Dean.....oops O_O
Do you even WANT me to start cataloging all of them?
Death: As old as God. Maybe older. Neither of us can remember anymore. Life, death, chicken, egg. Regardless -- at the end, I'll reap him, too.
Death: Before there was light, before there was God and the archangels there wasn't nothing, there was the Darkness. A horribly destructive amoral force that was beaten back by God and his archangels in a terrible war. God locked the Darkness away where it could do no harm, and he created a Mark that would serve as both lock and key, which he entrusted to his most valued lieutenant -- Lucifer. But the Mark began to assert its own will, revealed itself as a curse and began to corrupt. Lucifer became jealous of man, God banished Lucifer to Hell, Lucifer passed the Mark to Cain, who passed the Mark to you -- the proverbial finger in the dyke.
Cain: You find the blade, kill Abaddon, but make me a promise first. When I call you — and I will call — you come find me and use the Blade on me.
Dean: When he gave me the Mark, Cain said that this day would come, that after I killed Abaddon, I would have to come and put him down.
Hang on, my twitch is coming back. I'll have to take a break before I think of some more.