They will only spawn once you defeat a mechanical boss. They always generate light. A good way to kill them is using a large melee weapon (Such as a Breaker Blade) or a homing projectile. Spears, such as the Dark Lance, Mushroom Spear or Gungnir, provide a quick and easy way of killing these vicious pests.
Note that they can spawn even if you haven't entered Hard Mode and if you summon and defeat a mechanical boss.
They replace Hellbats almost completely after you defeat a mechanical boss.
- Added to the game.