Power of the Pit Fiend

You’ve manifested some of the power of a Pit Fiend, granting you the following benefits:

Ability Score Improvement. Increase your Strength, Constitution, or Charisma by 1, to a maximum of 24.

Pit Fiend's Defense. Your base armor class is 18, while you aren't wearing armor.

Pit Fiend's Resilience. You gain immunity to fire and poison damage.

Pit Fiend's Magic. You learn the fireball spell. You can cast this spell without expending a spell slot. Once you cast this spell in this way, you can’t do so again until you finish a long rest. The spell’s spellcasting ability is Charisma.

Fear Aura. Any creature hostile to you that starts its turn within 20 feet of you must make a Wisdom saving throw (DC 8 + your proficiency bonus + your Charisma modifier), unless you are incapacitated. On a failed save, the creature is frightened until the start of your next turn. If a creature’s saving throw is successful, the creature is immune to this feature for the next 24 hours.

Pit Fiend's Weapons. When you hit a creature with an attack made with a melee weapon, you can deal an extra 3d6 fire damage to the target. You can use this feature a number of times equal to your proficiency bonus, and you regain all expended uses when you finish a long rest.

In addition, your melee weapon attacks count as magical for the purpose of overcoming immunities and resistances to nonmagical bludgeoning, piercing, and slashing damage.