Chains of Asmodeus

Stage One Corruption: Beginnings

Once a character has attuned to a cursed infernal magic item or artifact, it begins the infernal corruption process. Each time that character finishes a long rest, they must make a DC 10 Wisdom saving throw. (If the character is a tiefling they have advantage on this saving throw.) On a successful save, the character suffers no effects, but the DC increases by 1 the next time they must make this saving throw. On a failure, the character progresses to Stage Two of their corruption unless the Dispel Evil and Good spell is cast on the character before they start their next long rest.

Breaking attunement to a cursed item prevents further Wisdom saves and resets the DC of the saving throw, if the character were to attune to the item again. However, if a character has already advanced into Stage Two of their infernal corruption, breaking attunement can no longer halt the process.

Stage Two Corruption: Sufferings

After failing the Wisdom saving throw in Stage One, the character progresses to Stage Two. While in Stage Two, they become delusional, seeing plots against them where there are none. Additionally, each time they rest, they experience terrifying visions and infernal whispers. Whenever they finish a long rest, they take 6 (1d12) necrotic damage, which ignores resistances and immunities and can't be healed until a Dispel Evil and Good or Remove Curse spell is cast on them. Once the character has taken this damage from their nightmarish visions six times, they progress to Stage Three of their corruption. While in Stage Two, the infernal corruption can be removed with one of the following spells: Divine Word, Heal, Mass Heal, True Polymorph, True Resurrection, or Wish.

Stage Three Corruption: Departings

Once a character's will has been significantly weakened, they progress to Stage Three. While in Stage Three, the character begins to suffer physical transformation, and slowly embraces evil. After they finish their first long rest upon entering Stage Three they must roll 1d10 to determine how the infernal curse has begun shaping them into a devil. In addition to the specific effects, a part-devil character is rendered infertile and the character detects as a Fiend when subjected to Detect Evil and Good spells and similar magic.

Following their devilish transformation, the character begins to experience waking whispers pushing them towards evil and they suffer terrifying visions whenever they rest, designed to completely break their spirit and push them further to evil. Each time they finish a short or long rest, the character must make a DC 10 Wisdom saving throw. If the character performed at least one evil act, such as an unprovoked killing of a creature, a manipulative deal, or making a decision that increased the suffering of others, they make the saving throw with disadvantage. When they fail the saving throw, they progress to the final stage of their corruption, Stage Four.

While in Stage Three, the infernal corruption can be ended with one of the following spells: True Polymorph, True Resurrection or Wish.

Stage Four Corruption: Finalities

After the complete devolution of a character's morals and will, they progress to Stage Four. When they finish their first long rest after reaching Stage Four, the character's alignment shifts to lawful evil. They're now bound by the devil's code, requiring them to honor any pact made and acquire souls in service of Asmodeus. Lastly, their physical form changes, morphing to resemble a devil chosen by the DM.

Once the character reaches Stage Four, the only two cures are the Wish spell, which counts as beyond the scope of the spell, or by signing an infernal contract with Asmodeus to reclaim their soul.