Conjure Minor Elementals (HB)

You conjure spirits from the Elemental Planes that flit around you in a 15-foot Emanation for the duration. Until the spell ends, you can use your bonus action to make a melee spell attack against one creature in the Emanation, dealing 2d8 damage. This damage is Acid, Cold, Fire, or Lightning (your choice when you make the attack). Additionally, when a creature you can see or hear ends its turn in the Emanation, you can use your reaction to make this attack against that creature.

In addition, the ground in the Emanation is Difficult Terrain for your enemies.

Using a Higher-Level Spell Slot. The damage increases by 2d8 for each spell slot level above 4.