Blade of Blood

You make contact with yourself or another and draw a blade of blood out of them, if the blade is from yourself you take 1d10 necrotic damage, if from another they must make a constitution saving throw, if failed they take 1d12 necrotic damage, if successful nothing happens. The blade of blood starts at 1d4 slashing damage, every hit it takes more blood dealing an extra 1d6 every hit, after the first hit the sword does 1d6 slashing, after the second it does 1d8, after the third it does 1d10, after the 4th it does 1d12, after the 5th it does 1d20, finally on the 6th hit it triggers and ruptures in the enemy dealing a final 1d20 plus 20 damage to the enemy.

The swords final hit damage increases by 1d20 for every level its casted above 3rd.