Kancho!
Fighting Style Feat (Prerequisite: 9th-level character, Fighting Style Feature or Martial Arts Class Feature) (Yaranaika)
Kanchō! (カンチョー) is a new secret option for Unarmed Strike. It can only be used if you have Advantage on the attack action. You clasp the hands together in the shape of a finger gun and poke at your unsuspecting target. You may yell "Kanchō!" when you attack. If you hit, in addition to unarmed damage and extra damage, target must make a Constitution saving throw against 8 + your Strength modifier + 2 × your Proficiency Bonus, or they will be Incapacitated with pain. An affected target repeats the save at the end of each of its turns, ending the effect on itself on a success. While target is in pain, another Kanchō hit on them only causes damage.
Kanchō adds extra damage, half the amount of a rogue of your level would inflict with a Sneak Attack, rolled down. So, the extra damage is 2d6 at 9th-10th level; 3d6 at 11th-14th level; 4d6 at 15th-18th level; and 5d6 at 19th level or higher.
If you have rogue levels, use your Sneak Attack damage, if it is higher than the extra damage inflicted by this feat.
Creatures with Unconscious condition, most Constructs, Undead, creatures without proper target area such as Oozes, and creatures unaffected by pain are immune to Kanchō. You still inflict damage but target does not need a saving throw.