Escalating Blast

Choose a creature or object you can see within range. A visible aura of rippling energy forms around the target, growing in intensity with each round. This aura remains visible even if the object or creature it targets becomes invisible. When this spell reaches the end of its duration, the aura releases an explosion of arcane energy. The base damage of this blast is 2d6 thunder damage. For the duration, at the start of each of your turns, the damage increases by 1d6.

When the blast erupts, it deals the accumulated thunder damage to everything within 30 ft. of the spell's target. Creatures in the area, including the the target of the spell if it's a creature, can make a Dexterity saving throw. A creature suffers the accumulated thunder damage on a failed save, or half as much on a successful one.

If the spell ends early, the blast erupts as described above, but the accumulated damage is rolled in d4's instead of d6's.

When you cast this spell using a spell slot of 4th level or higher, the starting damage increases by 2d6 for each slot level above 3rd.