Xozzath's Spear of Demise

You place your hands forward, 2 Black spikes 1meter long appear behind your shoulders, you yell a battle cry and they fly forward, impaling your enemies, and they start to scream in agony, the spikes drain their life force dealing 6d6 necrotic damage then returning one third of the damage dealt to you as HP. 
undeads take an extra 1d6 dmg and constructs take only half as much damage.

Creatures killed with this spell cannot be resurrected by anyone else except the user who killed them.

At Higher Levels. When you cast this spell using a spell slot of 8th or higher the damage increases by 1d6 for each slot level above 7th.