As a Magic action, you emanate a radiant light in a 30-foot Emanation that lasts for 1 minute or until you have the Incapacitated condition. Choose Aberrations, Celestials, Elementals, Fey, Fiends, or Undead.
Whenever the Emanation enters the space of a creature of the chosen type and whenever such a creature enters the Emanation or ends its turn there, it takes 4d6 Radiant damage. A creature takes this damage only once per turn.
Additionally, while in the Emanation, creatures of your choice have Advantage on saving throws against spells and other magical effects created by creatures of the chosen type.
Once you use this feature, you can't use it again until you finish a Short or Long Rest. You can also restore your use of it by taking 30 Radiant damage. This damage ignores Resistance and Immunity, and bypasses Temporary Hit Points.