Demon Spine

Demon Spine
Weapon (whip), very rare (requires attunement)

This long, jagged spine was ripped from the fresh corpse of a demon. The boney discs are eternally slick with crimson ichor, and an abyssal flame flickers from within, where the spinal cord would be. You have a +1 bonus to attack and damage rolls made with this magic weapon, and it deals an extra 1d6 fire damage to any target it hits. The demon spine has 7 charges, and it regains 1d6+1 expended charges after you complete a long rest.

Searing Laceration. When you attack a creature with this whip, you can expend one charge to make it a searing lash. If the attack hits, the creature is then marked with a searing laceration until the start of your next turn. Each time a lacerated creature is hit by an attack, it takes an extra 1d6 fire damage. If the creature is reduced to 0 hit points while it has a searing laceration, it erupts into an explosion of flame. Each creature within 5 feet of the exploding creature must make a DC 16 Dexterity saving throw or take 2d6 fire damage.

Demonic Fortitude. As a bonus action while wielding the demon spine, you can expend two charges to gain resistance to fire and poison damage for 1 minute. Additionally, all poisons affecting you are neutralized when this property is used.

Curse. Each time you expend one or more charges from the whip, you have a 5% chance of becoming possessed by Bilvemoz, the demon whose spine you are wielding. The possession lasts until you complete a long rest.
If you become possessed, the incorporeal spirit of Bilvemoz will enter your body and compete for control of your impulses. Each time you make a moral decision or roll initiative, you must make a DC 16 Charisma saving throw or do what Bilvemoz desires. Bilvemoz has an Intelligence of 15, a Wisdom of 15, and a Charisma of 15, and perceives through your senses while possessing you. Bilvemoz communicates telepathically with you and can speak, read, and understand Abyssal, Infernal, and Common. Bilvemoz can use your mouth to speak with a deep, vicious snarl. Bilvemoz seeks to corrupt mortals, slay devils, and takes wicked glee in forcing you to enact evil deeds when the opportunity arises, but is bored by anything else.

{Uncommon Variant}

Dormant Demon Spine
Weapon (whip), uncommon (requires attunement)

This long, jagged spine was ripped from the fresh corpse of a demon. The boney discs are eternally slick with crimson ichor, and a hellish flame flickers from within, where the spinal cord would be. The demon spine deals an extra 1d4 fire damage to any target it hits.

Demonic Fortitude. As an action while wielding the demon spine, you gain resistance to fire and poison damage for 1 minute. Once this property is used, it cannot be used again until you complete a long rest.

Curse. Each time you use the Demonic Fortitude property, you have a 10% chance of becoming possessed by Bilvemoz, the demon whose spine you are wielding. The possession lasts until you complete a long rest.
If you become possessed, the incorporeal spirit of Bilvemoz will enter your body and compete for control of your impulses. Each time you make a moral decision or roll initiative, you must make a DC 13 Charisma saving throw or do what Bilvemoz desires. Bilvemoz has an Intelligence of 15, a Wisdom of 15, and a Charisma of 15, and perceives through your senses while possessing you. Bilvemoz communicates telepathically with you and can speak, read, and understand Abyssal, Infernal, and Common. Bilvemoz can use your mouth to speak with a deep, vicious snarl. Bilvemoz seeks to corrupt mortals, slay devils, and takes wicked glee in forcing you to enact evil deeds when the opportunity arises, but is bored by anything else.

Cruel punishment from one demon to another; the owner of this backbone was reduced to a mere tool of pain.