Elder Rune of the Mad Mage
Bane Effect:
The target must make a Constitution saving throw (DC 22), taking 20d6 force damage on a failed save, or half as much damage on a successful one.
Boon Effect:
The target recovers its expended spell slots of 6th level and lower. If the target has no spell slots to recover, a magical shield surrounds the target for 1 hour instead. This shield grants the target resistance to all damage and can't be dispelled, though contact with an antimagic field destroys it.