The less dialogue the better. Speaking to Gordon in his office, whispering makes sense. On a rooftop, they can keep it at a bare minimum, with Gordon doing the talking. Do more scenes in their office than on a roof. Put Catwoman closer to him. It’s easy to pull off.
It’s true, if I was in Gotham, and I looked up to the top of a building, tree, whatever...it’s late...nobody around. And I see a massive shadowy figure that looks like wings hanging down, and ears. I’m going to freeze. Major chill up my spine and neck. Eyes watering “what the **** am I looking at!?”. The figure just stares. That’s more creepy than anything (btw I hope there’s a scene like this). If it were to speak, I’d imagine a spooky whisper would make matters worse lmao. Maybe a growling yell would break the spell instead. I’d still be creeped out but I think a whisper would be more effective and makes Batman come off like he’s always in control. He’s not upset, he just knows how **** will play out. So there’s a calm that surrounds him. Look at Michael Myers. The dude doesn’t speak and it’s way more terrifying. Less is more.