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: Most of the enemies at one time or another fall into this, though precisely which enemy varies from level to level. In short, if there's a jump over a bottomless pit, there will probably be an enemy waiting for you on the other side, and you'll get knocked into the pit if you just recklessly jump.