You could do a kaiju sort of thing, have it composed of different symbiotes with different attributes that could mature in time. It might also include grafted mechanical parts operates by a separate crew within the whole.
I could always suggest Battletech. I know it has a grim reputation as “too slow,” but I’ve always loved it and, knowing the rules, can crank out games pretty fast. And it has an in-built system for design, modification, and upgrading crews and pilots as they go.
This reply was modified 5 years, 7 months ago by Mr. Average.