"Gnome Bard" by Dean Spencer
*The Ground is Lava is a spell that first appeared in the 5e Campaign Setting Adventurer's Agency
The Ground is Lava:
Casting Time: 1 action
Range: 30 feet
Components: V C (a dried flake of brimstone)
Duration: concentration, up to 1 minute
A 5ft radius square of ground within range and that you can see becomes lava. The ground becomes difficult terrain for any creature that does not have an immunity or resistance to fire damage. All creatures within the area are dealt 1d6 fire damage whenever they start their turn in the magma, move through it, and when it first appears. This effect lasts for one minute or until the caster's concentration is broken. When the spell ends, the ground hardens and cools into black stone.