Armblade Punch Knife +3

Sap (Mastery): If you hit a creature with this weapon, that creature has Disadvantage on its next attack roll before the start of your next turn.

You have a +3 bonus to attack and damage rolls made with this weapon.

An armblade is a magic weapon that attaches to your arm, becoming inseparable from you as long as you're attuned to it. To attune to this item, you must hold it against your forearm for the entire attunement period. As a bonus action, you can retract the armblade into your forearm or extend it from there. While it is extended, you can use the weapon as if you were holding it, and you can't use that hand for other purposes.

Proficiency: simple, punch knife Source: Dungeon Master's Guide (2014) p. 213, Eberron: Rising from the Last War p. 276, Wayfinder's Guide to Eberron p. 120, Ben Huffman - Pugilist (Third Party)