For several shots they needed it to be raining, yet they were not able to film rain on location, so I had to track and simulate it as photo-realistically as possible.
It ended up being a mash of several simulations for each shot, the cameras were 3D tracked properly to allow for a little more of realism.
On other shots they could not film the bat colonies and they asked me to add them digitally, while also make them fly as realistically as possible.
I also made a 3D reconstruction of the locations in order for the shadows to move correctly.