The void dragon has 3500 hp with 0% physical resists, 150% tenebrium and 50% everything else. Poor guy isn't even poison immune.
It's really simple to kill it in 1 turn with just 2 party members:
- oath/wildfire/bless/rage/powerstance a dualwield warrior, autoattack
- lower will/soulsap/lower resist and throw arrow spray/dual or 2hander flurry/a master nonearth spell at it
