Lunar magic

Lunar magic was a tradition of magic wherein the potency of spells waxed and waned with the phases of the moon.

Training
Lunar magic could be learned by practitioners of arcane or divine magic, but they had to be followers of Selûne, goddess of the moon, or Mystra, goddess of magic.

Effects
For a practitioner of lunar magic, the level at which they cast spells or wielded innate spell powers rose and fell in tune with the lunar phase. When the moon was full, on the 30, 1, and 2 of each month, they experienced a slight boost. However, in the time of a new moon, on the 15, 16, and 17, when the moon was dark, they suffered a slight decline.

Practitioners
Lunar magic was commonly learned by members of the church of Selûne in and around Waterdeep. Demonstrating lunar magic was also typically a test of entry to the Order of the Blue Moon, an organization devoted to both Selûne and Mystra. It was definitely a requirement for the order's senior members, the Knights of the Blue Moon, such as Xale of the Starry Glen.

The moon knights, a militant order of Selûnite soldier-priests, also practiced a form of lunar magic, though it affected all their abilities, their capacity to turn undead, and even control over lycanthropy. The silver ladies, an order of Selûnite priestesses, practiced something similar, affecting the success of their divinations, immunity to lycanthropy, and even effectiveness against Shar-worshipers.

Views
Around 1372 DR, lunar magic was little known to scholars of the Art who studied the different ways to access and manipulate the Weave. Thus demonstrations of lunar magic drew much interest and attention from them.