I doubt there will be anything major as far as changes to gameplay, since cox said that anything you get in the DLC can be used in the main game. I think you'll probably gain a new ability such as the wings or boots that you can use optionally but I doubt theyll make a mandatory change to Gabriel in the DLC, cause then it would probably end ip being mandatory for the entire game. Any major gameplay changes are probably going to be in the sequel
I'm rooting for bat and wolf forms, and perhaps fireball or lightning magic