Way back when I was on CBM, I wrote what should be in Superman/Batman and one of them was Batman's first appearance being the first scene in the film. It went like this.
Start The Film In Gotham And With Batman
"In my opinion, Superman/Batman should start off like how Man of Steel started off. Just replace Jor-El and Krypton with Batman and Gotham City. I have an idea of how to do beginning. Most of my influence comes from The Dark Knight Returns, Batman: Gotham Knight, the intro to Batman: The Animated Series, 89 Batman, & the car chase scene in Spider-Man 2. Picture this. We start off with the opening like Man of Steel where you see the WB symbol, the DC symbol and the other production symbols. While you see that, you hear a police call going in about a robbery at the Gotham Bank. After you see the company logos, you see an overview of Gotham City. You start to go into and show around the city. Its nighttime. Its thundering and raining. We see the Batsignal up in the sky. We get to a building with a gargoyle and we see the back of Batman but never his front. We hear where the robberies are and what street their going on. Now for the record, they dont have to be just random robberies. You could replace them with Joker or Two-Face or anyone else. Someone more mob related. Or you can just have them be random robberies. Either way works.
Now back to where I was. We see Batman on top of a building. We see his cape flapping around. We then have Batman jump off the building and go to the robberies in a chase with police cars. We have them have a shoot out with a car with detective Harvey Bullock and Renee Montoya in it. We have the robberies in a van from the Bank. The robberies were able to shoot one of the tires of the police van off. They think that got away. We then see the driver ask the one of the guys is something following them since he saw a big shadow over them. We now see Batman in the classic Frank Miller pose like the photo I have above this topic over the van. We see him land on the front of the car. Batman punches from the glasses and the car spins out of control and crashes. The robberies didnt die and they get out and enter some abandon building.
There are like 3-4 thugs. We see them spread out. Batman takes one of them out front the ground like in The Dark Knight Returns. Other thug has his back against the wall and Batman grabs him and pulls him through the wall. We have another Batman knocks out. The final one is scared. We see Batman basically walk up behind him and disarm him and holds him up like he was about to integrate him. He knocks the thug out. The cops come to the building and we have the thugs tied to a stoplight pole. We then see move up to a building, like in the ending of Batman 89, and Batman is on top of another building on a gargoyle looking down. Zoom in around Batman. Have thunder boom and lighting strike a few times, end scene.
In that one scene alone, you already established how Batman is in this universe. You dont need to go into his training or his origin. We know Batmans origin. This opening is like how the opening was to the 89 Batman where at the end you say that Batman is a badass. If this was the opening and was pulled off perfectly, I promise no one would complain about Affleck being Batman."