Silvered Punch Knife

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.

Some monsters that have immunity or resistance to nonmagical weapons are susceptible to silver weapons, so cautious adventurers invest extra coin to plate their weapons with silver. You can silver a single weapon for 100 gp. This cost represents not only the price of the silver, but the time and expertise needed to add silver to the weapon without making it less effective.

Proficiency: simple, punch knife Source: Player's Handbook (2014) p. 148, Ben Huffman - Pugilist (Third Party)