* GameBreaker: 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.
* GoddamnedBats: Those skulls that float around and can follow the player. Better leave some mines where they're going to pass.
* TheyWastedAPerfectlyGoodPlot: The April Fools' edition could have been made into a nice alternate mode by simply making all guns have limited ammo.