Dark Slash

As a bonus action, you channel your own life force into your weapon. Granted that you have enough hit dice, you roll 1 hit dice + your Constitution Modifier per die, subtracting that value from your current Hit Points. This damage cannot be reduced in any way. On the next melee attack that hits an opponent you add double this amount to the damage dealt as Necrotic damage. This value can be doubled by a critical hit without increasing the damage you take, but you take the damage before you make your attack. After hitting an opponent, this spell ends.

At Higher Levels: when you cast this spell using a 2nd Level Spell Slot, you may increase the number of hit dice you roll by 1 for each Spell Slot above 1st.