The Void
Undead
What to know
The Void has 660 health.
It takes extra damage from spirit; it resists blunt, slash and pierce; poison does nothing to it at all.
Its only attack is ghost attack, 25 slash.
Of everything craftable, 
Lightning Strike, 
Frostfire Crossbow and 
Frostfire Sledge put the most damage through what it resists.
Spawn command
With devcommands enabled, this spawns The Void in front of you. The third number is the level: 3 spawns a 2-star.
Creature ID: Ghost_old · all console commands and IDs