These guys are one of the four enemies that weren't replaced with a flemoid. They do not appear in any of the normal levels, but are frequently encountered on the episodes 2, 3, and 4 of Doom. Because they have no sprites in Chex Quest, they are completely invisible and extremely hard to fight, though some OpenGL source ports make light appear when they are near. In Chex Quest 3 the Lost Soul is replaced with the Flem Mine.