- Demonic Spiders:
- No matter how tough, large and strong you are, you are pretty much over when a kobold immobilizes you with bolas or tanglefoot bag.
- Anything that transmits poison/disease by standing near you, like bone delvers or plagues of Whatever.
- Goddamned Bats: Many
- Shadow Oozes initiate a grapple every time they hit you, which means you can't run, use any large weapon and you get slowly strangled to death every round. They also heal at your cost and when you finally hit them, they just teleport shortly, hide in shadows and get another attack of opportunity against you. If you're a mage or someone else with bad eyes, run.
- Unless you're a priest, undead are resistant to critical hits (and by extension to one-hit kills), often have high natural armour and large hit point pool, so even spells won't get you far with them.
- Kobold-like monsters often wait for you in literall death-zones, have ridiculous dodging ability and throw tanglefoot bags, which means heavy armour classes can start rolling new character sheet once they get stuck.