Maegis

7-level Abjuration

You shatter a valuable shield, moving its thousand tiny pieces over the skin of a creature, a protective magic filling in the gaps between each piece forming its aegis. Until the spell ends, the target has resistance to all damage except force damage.   As an action, you can dismiss this spell and cause the aegis to explode. Each creature of your choice that you can see within 30 feet of the wearer must make a Dexterity saving throw. On a failure, they take 6d12 force damage, of half as much on a success.