* DemonicSpiders: Loads and loads of them - in fact, a key part of ''Angband'' strategy is just ''not to get into fights'' with creatures like these.
** Hummerhorns (giant wasps) have a horrifying combination of two abilities; a bite that causes confusion, and the ability to ''self-replicate''. If you have just one of these on your hands and you don't deal with it immediately, you're in for a world of trouble - its confusing bite will hinder you from acting while it happily replicates around you, surrounds you, and bites you to death. Even a high level player can be taken down by these if they haven't taken precautions.
** Zephyr hounds come in huge packs and have various breath weapons, which they won't hesitate to blast you with.
** Quylthulgs are immobile piles of rotting flesh with various teleportation abilities.
** Drolems are the reason you ''never'' go below 2,000 feet without poison resistance. They're dragon golems with powerful poisonous bites and breath weapons - and being golems, they're immune to many things that biological dragons wouldn't be.
** Ancient Multi-Hued Dragons, etc.
** "It moves [[LightningBruiser very quickly]]"
* GameBreaker: Like in most roguelikes, being fast. The most dangerous monsters are those that can hit you 5 times each time you move. The game is at least aware of this; the manual notes that speed is one of the most highly sought attributes to improve (and thus, speed enhancers are very hard to come by).
* GoddamnedBats: Oozes, icky things, mushroom patches, and worst of all, worm masses.
** Zephyr Hounds. Almost any time you see a "Z" on the screen (the earliest ones--Clear, Dark, and Light--are the sole exceptions) you'll want to cry.
* GoddamnedBoss: Smeagol is a low-level boss who isn't particularly dangerous, but is quite annoying; he has the toughness of a boss combined with the ability to steal your gold and teleport away. At the time you first encounter him, it's unlikely you'll be able to kill him, so your only option is to run or lose your gold.
** Wormtongue to a lesser extent, as he is actually threatening.
** Any boss that summons. Especially when those summons can (and do) summon.