Rage of the Hellfire [Heroic Feat]

READ THIS: This is a Heroic Feat. It cannot be taken normally with an ASI or chosen at 1st level by any race. Instead, any character can take it instead of their class' level 20 capstone ability.

The fire of the Nine Hells burns in your veins and enhances your combat strength with an unbridled heat that can reduce any opponents to charcoal. You gain the following bonuses:

• All of your weapon attacks and unarmed attacks deal an additional 1d10 fire damage that ignores fire resistance.
• You can cast fireball at 3rd level once per short or long rest without using any resources. If you are capable of spellcasting, you also learn this spell and you can cast it with your normal spell slots. If the spell hits yourself, you automatically pass the saving throw and take no damage from it.
• Whenever you reduce a creature's hit points to 0, they are instantly turned into a pile of ash. Nothing can save them from death, and they cannot be resurrected by anything except a true resurrection or wish spell.