Early style frame:
Based on location photo.
Alien robot gun designs:
#1 and #7 on the right were chosen.
Prop guns:
I didn't make these, they were made by some of the many talented people I work with, but never meet.
Gun light options:
Plate:
Matte painting:
Upper left lighting painted for fire to be added by compositor.
Painted 2D battle damage onto 3D model:
To save time, one robot was modeled in 3D, then 2D damage was painted to create variety.
Matte painting:
On left, added bullet holes, smoke damage, broken door, rubble. On right, created all damage.
work done @ The Mill
Final spot: