Earlier today, Stephen Totilo's review of Assassin's Creed II referenced the game's homage to Mario. Here's video of the fourth wall-breaking inside joke, which is so mainstream it's not inside. And it doesn't really break the fourth wall, either.
Well, never mind. I don't think it rates a spoiler alert, as no major plot devices or gameplay features are revealed. Here it is, courtesy of MTV Multiplayer.