In the Swamp of Evil, where the Misery Mire dungeon is located, there are three enemies that do not load properly, rendering them invisible. Despite this, they can still attack and take damage, though will remain unseen by the player.

These invisible enemies are Ku, some of which can be seen in the Swamp of Evil. The ones that do load properly are positioned in the deep water of the swamp, while the invisible ones are located in shallow water. It's likely the enemies were only programmed to function in deep water, and thus either the terrain was different during development, or the enemies were simply misplaced.