Vermin's Fang

The Pact with the Rat King, has left you feeling hungered, baring your teeth, savoring the taste of your last meal and salivating at the thought of meals to come. Upon drawing your blade and sacrificing some of your precious lifeblood, your weapons screeches; As a  crimson stain gives way to large, avaricious, and sharp teeth jutting haphazardly from every angle. Fangs ready to gnaw through steel and separate precious flesh from bone. 

Casting Vermin's Fang:

Costs: 1 BA and 1d8 damage-self. 

Time Limit: 1 hour

Upon casting your weapon grows a number of grotesque vermin teeth. Add 1d12 to your attack roll. 

At 4th and 6th level add an additional 1d12 damage dies. (4th 2d12, 6th 3d12) and so on from there. 

At 8th level double your Dexterity or strength bonus to hit and damage.

At 12th level add equal parts d12 damage of necrotic.

At 15th level triple the self-inflicted damage die 3d8. and hit a critical on nat 18, 19, 20.

At 18th level While this spell is active, you cannot be knocked unconscious while this spell is active. Any excess damage you take will result in an automatic failed death saving throw. But you will stay in the fight driven by the urge to feed.