Tormented Souls

The souls of many tormented adventurers and mobs finally had the buildup necessary to regain their vengeance on the world. Hostile to everything except for wither skeletons, these humanoid soul sand/soil entities are filled with pure rage and motivated by the urge to destroy everything around it. Inflicting fire damage and slowness, along with the ability to travel faster and whatever mobs it murders (eg, wall climbing, exploding without consequence, shooting projectiles) . Many civilizations have fortified their walls after realizing that the tormented souls have found their way to go to the overworld via portals. They instinctively find those over anything else, and will know no bounds to fuel its vengeance.