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: Any flying enemy can be this. They fly above your ordinary aim box, so you have to scroll up to shoot at them. Typically they fly past you before this can happen, so you have to struggle to keep them in your view. The fast-moving ground enemies can also be annoying.