I think we could add curses into los. You can read in the line that some creature curses you, but you don't notice anything.
I suggest you could add curses that you tick less hp for like 15 min (or even longer). other curses might be blindness (for a short time then), less xp for a creature, more chance to fail a hit/cast etc etc.
Instead of those evil curses you can add good curses (blessings), which do the opposite of evil ones.