any mech rpg that isn't lancer and is very free in what you pilot?

it's hard to describe, but basically in lancer it's very limited, very strict and so you can't just imagine something, you have to pick from a list of existing stuff and so Idk if there's any system that is made to allow for custom made stuff, that work around vibes and that could maybe be all theatre of the mind? but still with rules and overall a system