I'm hoping to kick off a post apocalyptic dark fantasy game where the setting on the surface is dark fantasy, but underneath it is set on a slowly decaying post galactic warfare isolated ringworld where te remaining rate sufficiently advanced tech is seen as magic but also various forms of "corruption" (Nanites, radiation,, warp engine leakage, or whatever handwavium you care to mention) gives characters mutant powers/magic.
Ideally Id like to use the same system for PCs but also for major NPCs and mutant creature/chaos nasties from the swamps of "don't go there".
What system from any BRP variant or supplement would people recommend for such a game and why?