Ansatsuken

Deadly Blows: Once per turn, when you make an unarmed strike or natural weapon attack and apply your sneak attack damage, as a bonus action you can attempt to make an additional attack. If the attack hits, you can add up to half of your sneak attack dice (round down) to the attack’s damage. You can do this a number of times equal to your proficiency bonus. You regain all uses on a long rest.