Fists of the Mantis Shrimp

Your long boxing practices against a barn door or a bag of sand has proved worthwhile. Your agility and the springiness of your tendons has allowed you to make lightning-fast punches with lethal speed. You have found the proper way to hold your hand for the hardest impact on flesh and bone, giving you the following benefits:

• Your Dexterity Score increases by 1 (up to a maximum of 20).
• Your unarmed strikes deal melee 1d4 thunder damage plus your Dexterity modifier, instead of bludgeoning damage.
• When making melee unarmed strikes you roll your attack with advantage.
• When you drop a creature to 0 hit points with a melee unarmed strike attack, you can choose to knock them out. They are unconscious and stable, but you scar them permanently, usually leaving a dent or impression to their skull. They regain one hit point in d8 hours but their hit point maximum is permanently reduced by your Dexterity modifier.