Path of the Eruption

See class features to get an idea.

Volcanic Rage

Starting at level 3, when you rage, volcanic power erupts from you for devastating effects. When you activate rage, you may also cast the spell Scorching Ray at second level. For the purposes of this spell, your spell attack modifier is Constitution + your Proficiency Bonus. Additionally, all attacks you make while raging are counted as magical. While raging, you deal an extra 1d6 fire damage whenever you hit with a melee weapon attack.

Fiery Presence

Beginning at 6th level, you gain the ability to frighten and burn those who touch you. As a reaction, when you are hit with a melee weapon attack, you may choose to deal an amount of fire damage equal to 2 times your level to the creature who hit. When dealing this damage, immunity to fire damage is counted as resistance instead, and resistance is ignored. Additionally, if you drop a creature to below half their maximum hit points, or they were already below half their maximum hit points, they must succeed a DC 13 wisdom saving throw or be frightened of you for a minute.

Tremor rage.

Starting at 10 level, your rage shakes the ground. Whenever you activate your rage, you may choose any number of creatures within 30ft of you. They must all make a DC 18 Dexterity saving throw. On a failed save, they fall prone and take 2d10 bludgeoning damage, on a successful save they take half damage, and do not fall prone.

Eruption

Starting at 14th level, your rage becomes world-shattering. When you activate your rage, choose any number of creatures within 60ft of you, they must make a Dexterity saving throw. On a failed save, they take 14d8 fire damage, taking half as much damage on a successful save. When dealing this damage, immunity to fire damage is treated as resistance, and resistances to fire damage are ignored.