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.
Good Bad Bugs: If you kill the first three baddies in level two quickly enough, the level will count itself as completed even though there's three more baddies waiting to spawn in.
That One Level: The third level of the game is you at the end of a hallway, without a weapon. The weapon is at the other end, sitting in front of three enemies shooting at you. You have to dodge, duck, dip, dive and dodge their bullets to reach it. Easily the most difficult level (for the time being...).