Fun fact: Batman: Arkham Knight actually has more than one introduction sequence. There's the one you see normally. And there's the one that can only trigger under certain special conditions.
Reader Brandon tipped me off to a special intro within Batman: Arkham Knight, and it's actually super cool. You can view it here, courtesy of Dtoxz324. Headphone warning -- things get loud for a few seconds:
So here's what happens (skip to the 3:50 mark if you want to get to the meat of it). NORMALLY, the game starts with you burning the Joker's body. Any button you press at the start intensifies the flames. But if you start a new game plus, you instead get an intro where the Joker comes alive, screams, and says "this is how it happened. This is how the Joker died." Neat, huh? And thematically consistent with what the rest of the game is about, but I won't spoil those details for those of you that haven't gotten far enough in yet.
Here's the normal intro via IGN, for comparison's sake:
Right now, it looks like the alternate intro is only possible for people who have beaten the game at least once. The reader who told me about it only found it after going into new game plus, and I had someone else who has beaten the game confirm that this happens in new game plus. I on the other hand have not been able to trigger it, and I haven't beaten the game. UPDATE: Readers tell me this happens if you start a new game, period.
My favourite part about all of this is that the secret intro almost acts like a jumpscare:
Damn, Joker. You got me good.