Allow it to be controlled by it's own, sentient AI, capable of taking its own choices, and allow it simple instincts and skills, such as walking, hunting, and all that. Make sure the AI seeks for ever more victims, and release them in, for example, a city of opposing forces, or certain "zones".
Like a minefield. But instead of exploding, they hunt you down and f--k up your day.
In case they escape the "zone", a small selfdestruct system in either the robot or the core of the AI. One click, escapee shuts down, one way or another.
I spend too much time on coming up with unlikely torturing devices for unknown futuristic armies. Stuff like this sorta comes naturally for me. It's fun, but sorta... Weird, too.
Currently sketching out tanks that are able to climb mountains/buildings to "snipe" with the main barrel. Tank-snipers... I think just the look of those in the distance might already be enough to scare off some intruders, no?
Well, anyway, amazing work, the painting looks great, as well as all of your work, of course. Stuff like this is the reason for me to try painting...