Darkfire

You summon a blaze of darkfire to your hand. Darkfire emits no light, but produces the same heat as a regular fire, and it is invisible except to those with darkvision. While you hold the darkflames, it doesn't harm you or your equipment, and you have several options, which can be taken immediately or performed as an action on a later turn:
Touch. Make a melee spell attack against a creature within 5 feet of you. On a hit, the creature takes 3d10 Fire and 3d10 Necrotic damage.
Hurl. Make a ranged spell attack against a creature you can see within 90 feet of you as you hurl the blaze of darkfire at it. On a hit, the creature takes 3d10 Fire and 3d10 Necrotic damage.
Breathe. You breathe in the darkfire, then exhale it in a 30-foot-cone in front of you. Creatures in the area must make a Dexterity saving throw, with disadvantage if you are in darkness when you breathe out the flames and they do not have darkvision. Creatures that fail the saving throw take 3d6 Fire and 3d6 Necrotic damage. If they succeed, they take half as much.
When you use any of these options, the darkfire is extinguished, and the spell ends.

At Higher Levels. When you cast this spell using a spell slot of 5th level or higher, the Fire and Necrotic damage increases by 1d10 per spell level for the Touch and Hurl options, and by 1d6 per spell level for the Breathe option.

(I found this spell in a homebrew class PDF created by Almir Eldignor, and he deserves the credit for the idea.)