Ethereal Flinch

As the serum takes effect, your feel your body at times spasm briefly to the ethereal plane, and you feel a heightened awareness to quick movements near your person.

You can use this ability as a reaction to cause an enemy to have disadvantage on it's attack roll against you. You must decide to use this before learning the result of the enemies attack roll.  Once activated, this ability lasts until the end of the current enemies turn, and cannot be used again until after your next turn. This property cannot be activated while you are incapacitated, restrained, or otherwise unable to move

You may use this ability a number of times equal to your proficiency bonus plus one, per short rest.