Wither Skeleton

Wither Skeletons naturally spawn in nether fortresses. They don't catch fire and immune to lava. They inflict wither debuff for short time. They quite fast and they can't pass through 2 blocks. They are Undead Mobs. They have chance to drop stone sword (badly damaged),bones 0-2,coal 0-2 and rarely wither skeleton skull which used to summon Wither Boss.