Opus of Elemental Substance

Fulminate

8-level Evocation

With a gesture and a word, you enshroud one creature in range with blistering arcs of lightning. The target must make a Dexterity saving throw, taking 12d8 lightning damage on a failed save or half as much on a successful one. On a failed save, the target is also suffused with crackling lightning for the duration. Creatures wearing medium or heavy armor, or creatures composed mostly of metal, have disadvantage on their saving throws against this spell.

Lightning sparks and flickers along the surface of the target and sheds dim light in a 10-foot radius. At the end of each of its turns, the target repeats the saving throw, taking 6d8 lightning damage on a failed save. On a successful save, the spell ends.

When you cast this spell using a spell slot of 9th level, the damage increases by 3d8 and the duration becomes 10 minutes.