D'khrun's Patient Strike

You channel your energies over time into your weapon, readying it for a deadly strike. For the duration, your weapon is coated in a sheen of magic. The spell automatically ends if the weapon leaves your hand.

The weapon enhanced by this effect deals an additional 1d6 lightning damage on its next successful strike. If at the end of your turn you did not hit with this weapon, the damage increases by 1d6, stacking for a maximum number of rounds equal to your spellcasting ability modifier. Additionally, as part of the action used to cast this spell, you may make a single weapon attack with the enhanced weapon.

The initial damage, and the additional damage at the end of every round, increase by 1d6 at 5th, 11th, and 17th level.