Hey, I also recently built Kai's Fire mech, and was actually just building the lightning jet today, just waiting on a parts order tomorrow to finish it.
May I ask, did you find a way to attach the Fire Mech's arms without them falling off? (gravity seems to only hold for a bit before they slide clean off)
Nice!! I might try this or the water strider next since I'd need custom parts for the quake mech/dragon mech