Moonbeam

When the Cylinder appears, each creature in it makes a Constitution saving throw. On a failed save, a creature takes 2d10 Radiant damage, and if the creature is shape-shifted (as a result of the Polymorph spell, for example), it reverts to its true form and can't shape-shift until it leaves the Cylinder. On a successful save, a creature takes half as much damage only. A creature also makes this save when the spell's area moves into its space and when it enters the spell's area or ends its turn there. A creature makes this save only once per turn.