Vhalzrax's Infernal Deluge

A fiery portal tears open above a point you can see within range, unleashing a torrent of sticky magical flame. Each creature in a 15-foot-radius Sphere centred on that point must make a Dexterity saving throw. A creature takes 3d8 Fire damage on a failed save, or half as much damage on a successful one.

A creature that fails the saving throw is wreathed in magical flames. At the end of its next turn, it takes an additional 2d8 Fire damage as the flames continue to burn before dissipating.

Flammable objects in the area that aren't being worn or carried begin burning.

Using a Higher-Level Spell Slot. The initial damage increases by 1d8 and the lingering damage increases by 1d8 for each spell slot level above 3.