Immolate: 9th Level Spell

[iheartwalrus]

Hi there, I'm new to homebrewing and I'm looking for help in balancing a custom spell I've made.

Immolate (9th level Evocation)

Casting Time: 1 Action

Range: 120ft

Components: V, S, M (a chunk of obsidian and a ruby worth 2000gp

Duration: Concentration, 1 minute

The ground in a 50x50 cube is instantly turned into molten lava. All creatures that are exposed to the lava have their movement speed reduced to 5 and take 5d6 fire damage at the beginning of each round. They also have disadvantage on any ability checks or attacks made. A Dexterity saving throw (caster's Spell Save DC) halves the damage. The creature stops taking damage once they have used their movement to escape from the lava or are removed from it through other means.

Any suggestions on how to balance this?

[Ninja_Prawn]

Hi there, I'm new to homebrewing and I'm looking for help in balancing a custom spell I've made.

Immolate (9th level Evocation)

Casting Time: 1 Action

Range: 120ft

Components: V, S, M (a chunk of obsidian and a ruby worth 2000gp

Duration: Concentration, 1 minute

The ground in a 50x50 cube is instantly turned into molten lava. All creatures that are exposed to the lava have their movement speed reduced to 5 and take 5d6 fire damage at the beginning of each round. They also have disadvantage on any ability checks or attacks made. A Dexterity saving throw (caster's Spell Save DC) halves the damage. The creature stops taking damage once they have used their movement to escape from the lava or are removed from it through other means.

Any suggestions on how to balance this?

Before I get to balancing...

• There's already a spell called Immolation in the Elemental Evil Players Companion. Also I'd argue that this one doesn't really immolate people anyway; I'm sure you can find a better name.
• 'Exposed to' is poorly defined. I'd change it to 'any creature that starts its turn in the lava'.
• Reducing speed to 5 feet is a bit unusual. First of all, you should specify that it only applies to base walking speed. Then I'd consider whether it shouldn't just be 'halved' as if the lava was difficult terrain, or something similar.
• You need to specify when the disadvantage ends. Is it when they leave the lava? When they succeed on a save? When the spell ends?

Balance-wise, this does not justify 9^th level. Not even close. It's not powerful enough or flexible enough. It's probably on par with Fire Storm, a 7^th level spell. For comparison, here's my Transmute Lava spell:

Transmute Lava
9^th-level transmutation

Casting Time: 1 action
Range: 120 feet
Components: V, S, M (clay and water)
Duration: Concentration, up to 10 minutes

You choose an area of stone or lava that you can see that fits within a 40-foot cube and that is within range, and choose one of the following effects.
__Transmute Stone to Lava. Nonmagical stone of any sort in the area becomes an equal volume of thick and flowing lava that remains for the spell’s duration and sets fire to any flammable material it comes into contact with. If you cast the spell on an area of ground, any creatures in that area begin to sink into it. Each foot that a creature moves through the lava costs 4 feet of movement, and any creature on the ground when you cast the spell must make a Strength saving throw. A creature must also make this save the first time it enters the area on a turn or ends its turn there. On a failed save, a creature sinks into the lava, takes 10d10 fire damage, and is restrained, though it can use an action to end the restrained condition on itself by pulling itself free of the lava. On a successful save, or when a creature uses its action to pull itself out of the lava, the creature takes 5d10 fire damage. If you cast the spell on a ceiling, the lava falls. Any creature under lava when it falls must make a Dexterity saving throw. A creature takes 4d8 bludgeoning damage and 10d10 fire damage on a failed save, or half as much damage on a successful one.
__Transmute Lava to Stone. Nonmagical lava or magma in the area no more than 10 feet deep transforms into soft, cool stone for the spell’s duration. Any creature in the lava when it transforms must make a Dexterity saving throw. On a failed save, a creature becomes restrained by the stone. The restrained creature can use an action to try to break free by succeeding on a DC 20 Strength check or by dealing 25 damage to the stone around it. On a successful save, a creature is shunted safely to the surface to an unoccupied space.