These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Goddamned Bats: Goblins. Especially if you don't set up lights. You will suddenly find your mine overrun by stack of 20+ goblins.
Good Bad Bugs: If a dwarf is mobbed by a stack of enemies too big for the engine to handle, it pretends combat was never going to happen. A blessing, because if you're that overwhelmed, you've probably been stuck in a death cycle for several turns anyway.