You have learned to harness elemental energy and channel it into your melee attacks. Choose one of the following damage types; acid, cold, fire, or lightning. Once per round when you hit with a melee attack, you can choose to channel that element into the strike, dealing an additional 1d6 damage of the chosen type. This additional damage increases to 2d6 at 6th level, 3d6 at 11th level, and 4d6 at 16th level.

Once used, roll a d6 at the start of your turn. On a roll of 5 or 6, you regain use of this ability.