I'm still mentally scarred by Ghosts in Might and Magic II. I remember their touch causing characters to age 10 years. I remember fighting to a fountain to get back some years, it having the reverse effect, and eventually giving up the game because all my characters were dying of old age. Still annoys me to this day.
Also, as a longtime campaigner I always dreaded creatures whose XP reward was way out of line with the risk. The Wight example is great. They can steal 10,000 xps that took months to get, and if you beat them, you get 1400 or so xps divided by the number of members of your party. Say what you want about Iron Golems and Beholders, but at least the risk was worth the reward. Wights, rust monsters, and poison spiders put up a huge risk with a minimum xps and garbage treasure.
Also, as a longtime campaigner I always dreaded creatures whose XP reward was way out of line with the risk. The Wight example is great. They can steal 10,000 xps that took months to get, and if you beat them, you get 1400 or so xps divided by the number of members of your party. Say what you want about Iron Golems and Beholders, but at least the risk was worth the reward. Wights, rust monsters, and poison spiders put up a huge risk with a minimum xps and garbage treasure.