Towards the end of this episode on of the Winchesters says "I can't believe Crowley has a son." However in an earlier episode they summon the son to help fight Crowley. Season 6 episode 4."Weekend at Bobby's."
When Dean is kneeling over Abadon pounding her with the First Blade in his hand the blade's pointing to the right. As he's punching they pan to Sam then back and blade is flipped in his hand and pointing to the left.
At approximately 12:30, Sam mistakenly calls Dean "Sam".
Gavin is from the past and yet he clearly has a hole in his chin from a piercing.