Judging on how Dean makes fun of him for it, I'm willing to bet it was Dean who told Sam that the Easter Bunny didn't exist. I doubt it had anything to do with the Santa-incident though, since I don't think Dean actually even noticed that he was the one that told Sam that Santa didn't exist. But, that's just my opinion. :P

I'm up for an inverted parallel of the S8 finale for sure.

As for Jared pranking Dylan - As you say, I think Dylan was saved by the fact that the last time he was on, he didn't have screen time with Jared...which means that this was Dylan's "first" episode with Jared, so Jared was probably still in nice mode. ;)