Calculated Retribution
You surround yourself with a dampening magical field and collect the energy of a foe’s attack to use against them. When you take damage from a weapon attack, you can end the spell to halve the attack’s damage against you, gaining a retribution charge that lasts until the end of your next turn. By expending the retribution charge when you hit with a melee attack, you deal an additional 2d10 force damage.
You may use your reaction to halve the damage of an attack against you up to a number of times equal to the level of the spell slot used, gaining a retribution charge each time that lasts until 1 round after the spell ends. You must still make Constitution saving throws to maintain your concentration on this spell, but you do so with advantage , or if you already have advantage, you automatically succeed.