Combat Mastery, Variant (5e Feat)
From D&D Wiki
You trained hard. You gain the following benefits:
- Weapons you wield acquire the versatile property.
- Whenever you wield a weapon with the versatile property, you increase the category of the damage die by one. For example, a long sword would deal 1d10 slashing damage, instead of the traditional 1d8 slashing damage. The damage type remains the same.