YMMV: Angband

  • Demonic Spiders: 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 very quickly"
  • Game Breaker: Like in most roguelikes, being fast. The most dangerous monsters are those that can hit you 5 times each time you move.
  • Goddamned Bats: 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.
  • Goddamned Boss: Smeagol. Wormtongue to a lesser extent, as he is actually threatening.
    • Any boss that summons. Especially when those summons can (and do) summon.