Batman v Superman production designer Patrick Tatopoulos has shared concept art of a bat thing (not Man-Bat, I don't think) that was originally literally going to be part of Bruce Wayne's nightmares. It will be part of mine, now. If you click this, don't say I didn't warn you.
I don't think it's a huge shock that the concept art below was for a monster meant to show up in that same "Knightmare" scene as evil Superman and his insect soldiers. It was a pointless moment meant to foreshadow future movies, but wasn't actually relevant to the movie it was in. At least since the scene was already so absurd, a giant evil bat-creature wouldn't have been out of place.
Tell me you don't look at this picture and hear, "Give us a kiss!"
Bleah. This is the villain that movie truly needed to scare people for years to come.