I've deduced & tested that poison deals 5% of your/your enemies health per turn, so if you ever want to know how much health an enemy has -- poison them, see the damage, & multiply it by 20 !!

(p.s, I fucking love this game! it has so much charm. It's also way longer than I was expecting it to be, which is a good thing. My humble suggestion is to add some sort of fast travel mechanic, because backtracking (especially late game) can get pretty annoying)