I wanna run a Witcher 3-esque game. I would ideally like to incorporate elements of "Knowing what the miniboss monster can do and is weak to is important, if not vital/crucial," along with "Goblin equivalent may be less dangerous to you now, but it will always be dangerous" and a touch of "Magic is powerful and very few people have access to undiluted magic." What system would you reccomend?
Depends.
If you want knowing the fiddly details of the monster’s abilities and weaknesses to be critical on a tactical, blow-by-blow level, that’s basically Dungeons & Dragons 4th Edition’s wheelhouse. It’s hands down your best option if you want to capture the juxtaposition between deliberate, positioning-is-everything tactics and exuberant fantasy-martial-arts wackiness that you see in games like The Witcher. (As always, my D&D-related recommendations are edition-specific; D&D is half a dozen completely different games that just happen to share a title, so they’re not interchangeable.)
Conversely, if you’re talking about higher level investigative play, and you don’t mind combat being pretty abstract (i.e., to the point that a whole fight might be resolved with a single roll), you might have a look at Monster of the Week. It’s got a present-day setting, so you’ll need to do a bit of hacking to use it for The Witcher, but the affected bits of the system are light enough that it’s not going to be too onerous - mostly just reducing the number of guns on the playbooks’ gear lists. It’s probably a better option for the “rare magic” thing, too, since the system has no baked-in presumption that magic-using characters are common; in fact, it’s an explicit rule that playbooks are unique, so if somebody decides to be a wizard, they may well be the only one in the world.
