Moonlight Guardian

The guardian is immune to any spell or other effect that would alter its form.

The guardian has advantage on saving throws against spells and other magical effects.

Whenever the guardian is subjected to radiant damage, it takes no damage and instead regains a number of hit points equal to the radiant damage.

The guardian makes two Moonlight Slam attacks.

Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 8 (1d8 + 4) bludgeoning damage plus 4 (1d8) radiant damage.

The guardian unleashes a magical blast of moonlight in a line 60 feet long and 5 feet wide. Each creature in that area must make a DC 14 Dexterity saving throw. Creatures that aren't in their true form have disadvantage on the save. On a failed save, a creature takes 22 (5d8) radiant damage, and if it isn't in its true form, it is forced into its true form and can't change forms until the end of the guardian's next turn. On a successful save, a creature takes half as much damage only.