Trivia: Just before Protocol 10 starts, you end up in a giant fight with Joker and a good number of his goons. If you activate Detective Vision during this fight, you'll see that Joker doesn't have a skeleton. This is also true when he's holding Talia hostage in front of the move theater. This offers a hint to how the plot plays out.
Trivia: In addition to Black Mask, there are two other cameos in the game's intro sequence. When you're making your way through the prison line, one of the prisoners says to Bruce, "You're on my list," and pretends to shoot him with his finger. This is Deadshot, who would later appear in one of the game's side missions. A little bit later, after you go through the armored door, look up at the roof of the building towards the right. You can see Azrael, who disappears in a puff of smoke. Again, he later appears in one of the game's side missions.