Brimstone Fury

You are filled with the wrath deep within you, flames flicker from brimstone in your eyes.

When a creature successfully damages you, as a reaction you can build up fury. 

You can have a maximum of 3 fury stacks. 

Using a bonus action, you can reflect the damage off of your last reaction to the attacker. This damage is multiplied by each stack to a maximum of 3 times. The damage type is what the last person who attacked you used.

You can build up fury by spells, but can only reflect an actual weapon attack (i.e. from a sword, unarmed strike, but not something like sneak attack).

As you invoke your fury on another soul, you begin to feel sluggish. Until the beginning of your next turn, you subtract your fury stack amount from your AC.