Keranos’s Devotee

Piety Trait

Piety 3+ Keranos trait

As a devotee of Keranos, you have proven your wisdom and your allegiance to the storm lord. Once on each of your turns when you hit a creature with a weapon attack, you can deal an extra 1d6 lightning damage to the target. You can use this trait a number of times equal to your Intelligence modifier (minimum of once). You regain all expended uses when you finish a long rest.

Source: Mythic Odysseys of Theros p. 55