Just picked him up and felt he needed an arm cannon. His long sword was all twisted up from being tied down in the package, so I cut the blade off and kept the barrel section. I plugged it into the big gray cannon from the Constructbots Optimus set, and driller a hole into his forearm:
EDIT- I attached his tread to the cannon to make an ammo/energy belt (and, unrelatedly, moved the hip kibble to his backpack):
Also fits in tank mode. Not sure I like the blue part on top, but I wanted to keep all the parts on board.
Thanks for looking!