Vampiric strike

Your strength and affinity to arcane magic allows you to repurpose your foe's energy to be your own. Before attacking, cast this on a weapon of your choice as a bonus action. On a successful attack, roll damage as normal, then roll 1d8. Divide the roll by 20, and heal that percentage of damage from yourself, rounded to the nearest whole number. This applies to one attack, not one weapon - use total damage for a multi weapon attack. At higher levels, add +1 to the d8 roll per slot above first. After 2 rounds, the magic dispels.

Ex. I cast at 3rd level. I deal 27 damage with my attack, then roll a 6 + 3 = 9, meaning I heal 9/20 = 45% of 27, which is 12.15, rounded up to 12 health healed.