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.
YMMV: Super Crate Box
Game Breaker: The Revolver in the April Fool' version, with the Flamethrower a close seconds. Once you take them, as long as you avoid getting more crates, you can just find a safe spot and die of boredom before any enemy is able to touch you.
Goddamned Bats: Those skulls that float around and can follow the player. Better leave some mines where they're going to pass.