Book: Mantra's Guide to Exorcism and Possession

Within these pages lies hard-won knowledge gleaned from battlefields, haunted ruins, and cursed sanctuaries. Mantra’s Guide offers adventurers practical wisdom for identifying, resisting, and banishing hostile entities that seek to corrupt mortal minds and bodies. While demonic and diabolical possessions are the most prevalent—and often the most catastrophic—one must not underestimate the subtle invasions of the Feywild or the chilling grip of incorporeal Undead. Any spirit with intent and the power to cross thresholds, including ghosts with the Immaterial Movement trait, may attempt possession. Vigilance, piety, knowledge, and preparation are your only true safeguards.

Possession

Innate ability shared by some Fiends, Fey, Celestial, and Undead

The DM may grant this ability to any creature with incorporeal or extraplanar qualities for narrative reasons. Celestials rarely use Possession, preferring to respect free will—but it has been known to occur under extraordinary circumstances.

Prerequisites

• Possessor must be at least CR 2 and on the same plane of existence as the target.
• Must see or hear the target.
• Undead must have Incorporeal Movement or a similar trait.
• Fiends/Fey/Celestials lacking this trait may be temporarily empowered to phase
  into the target.
• Target must fail two saving throws: a Wisdom save and a Charisma save (see below).
• Multiple entities may attempt to possess the same host. They may either battle for dominance or cohabit, requiring separate expulsions.

Possession (Recharge 5-6). Wisdom Saving Throw: DC 10 + ½ the possessor’s CR, one creature or object the possessor can perceive within 5 feet (see or hear).

Saving Throw Modifiers:

Immunity. If warded by Protection from Evil and Good, inside a Magic Circle, or protected by the Hallow spell or special magic items.  

Advantage. Good-aligned creatures, creatures Immune to the Charmed Condition, or those with more than 100 Hit Points.

+2 Bonus. Creature wearing with faith the holy symbol of a Good-aligned deity or powerful Warlock patron. This symbol can be emblazoned on a shield.  

Disadvantage. Creatures that serve or worship an evil entity, or that have recently committed grievous acts, practiced dark magic, or has a Corruption score of 7 or higher. 

Failure (object):

A possessed Object becomes Cursed and uses the Poltergeist or Animated Object stat block in combat. It radiates a cursed, befouling presence. Anyone touching the object must succeed on a DC 15 Wisdom saving throw or become cursed as per a Bestow Curse or Witch’s Curse spell.

Failure (creature):

Incapacitated until the end of its next turn and take Psychic damage equal to the possessor’s Challenge Rating. Failed save by 5+: also Unconscious for that duration. If reduced to 0 HP by this damage, drop to 1 HP instead.

At the end of target’s next turn, the creature makes a Charisma saving throw (same DC). Success: Possession ends, but creature is Slowed until end of next turn. Failure: Possession takes hold; target creature gains the Possessed condition.

POSSESSED [CONDITION] ᴮᴹ

While you have the Possessed condition, you experience the following effects.

Effects on the Host
Charmed. You are Charmed by your possessor.
Dual Nature. You count as both your normal creature type and the possessor’s creature type for the purpose of spells and effects.
Shared Resilience. You gain Resistance to one damage type the possessor resists or is immune to (DM’s choice).
Alien Intellect. You adopt the possessor’s Intelligence score and saving throw modifier, if they are higher than yours.
Vulnerable Vessel. The possessor can attempt to seize complete control of your body (see Control, below).
Molded Personality. For each week you are possessed, you gain a new personality trait or character flaw related to your possessor's identity. 

Effects on the Possessor
Ethereal Presence. The possessor cannot be directly targeted by attacks or spells while within you, except by effects that specifically affect both its creature type and its incorporeal essence. Spells or abilities that require sight cannot target it unless the attacker can perceive its hidden form, such as Divine Sense or Truesight.
Boon or Bane. At will, the possessor can grant a +1d4 bonus or impose a –1d4 penalty to any d20 test you make.
Mind Probe (2/day). The possessor may probe your surface thoughts and memories, as if casting Detect Thoughts. You can resist with a Wisdom saving throw.
Control (3/day). The possessor may fully control your body for 10d10 minutes (no saving throw), using its own Intelligence, Wisdom, Charisma, and skill proficiencies. 

While Controlled 
Helpless Awareness. You remain conscious of your surroundings but cannot act, speak, or move unless allowed by the possessor. 
Alignment Shift. Your alignment temporarily shifts to match the possessor’s.
Borrowed Tongues. You understand and can speak the possessor’s languages.
Surface Only. The possessor cannot access your deepest memories or secrets, only surface thoughts and emotions, except with its Mind Probe ability (see below).
During Combat: Each time you take damage while controlled, you may attempt a Charisma saving throw. On a success, the possession is suppressed for 1 minute.
Persistent Resistance: If you succeed on three of these saves within 24 hours, the possessor cannot attempt to control you again until you complete a Long Rest.

Suppressing the Possession
Rest Resistance. After each Long Rest, you may repeat the Charisma saving throw. On a success, the condition is suppressed until the end of your next Long Rest. You make this save with Disadvantage if you are on an Evil-aligned Outer Plane.
Moment of Defiance. If compelled to act against your values, you can use your Reaction to attempt a Charisma saving throw. On a success, the condition is suppressed for 1d4 hours.

A saving throw DC equals 10 + half the possessor's Challenge Rating (minimum 12). 

Ending the Condition
Possessing entities are expelled from bodies through divine spells or rituals, such as en exorcism.

Other Suppression Methods

These methods can suppress the effects of the Possessed condition for a limited time.

• Ceremony (Atonement ritual) : 3d12 hours
• Bless, cast using a spell slot equal to or higher than the CR of the possessing entity : 1d10 minutes
• Greater Restoration : 48 hours
• Remove Curse : 24 hours
• Holy Water or taking at least 10 Radiant damage: 1d10 minutes, or until you roll a 1 on a d20 Test during combat (whatever comes first).

Concealing the Possession

A possessing entity can, at any time, speak mentally to the Possessed creature in a language that the creature understands. But the Possessed creature may not always know that it is Possessed. The possessor can make an Intelligence (Stealth) check to hide its possession, contested by the Possessed creature’s passive Insight score.

Discreet Possession. If the creature’s passive Intelligence (Stealth) score is higher than the creature’s passive Insight score, then the creature doesn’t become aware of its possession unless the possessor forces it to act in a manner contrary to its core values, or if someone else discovers the possession by its effects on the creature’s behavior.

Awareness Suppression. As an action, the possessor can attempt to suppress the target’s awareness (consciousness of surroundings). The target must make a Charisma Saving Throw:

• On a success: The target remains aware, and the possessor takes 11 (2d10) Psychic or Radiant damage (DM’s choice). It can’t attempt awareness suppression again for 1 hour.
  If the Psychic or Radiant damage reduces the possessor to 0 Hit Points, the possessor is killed, disappearing in sulfurous smoke or leaving behind some demonic ichor, gaining a new body instantly if it died outside its native plane, and the Possessed condition ends.
• On a failure: The target is unaware for 1d4 hours, during which time the possessor can take total control of its body (assuming it still has one of its 3 Control uses remaining). When the target regains its awareness, it has no memories of that time.

Exorcism 

Entities are expelled from bodies through divine spells or rituals.

Banishment (4th-level Abjuration) (BM version)

1 action, range 30 feet.

One Aberration, Celestial, Elemental, Fey, Fiend, Monstrosity, or Undead you can see within range must succeed on a Charisma Saving Throw or be transported to a harmless demiplane for the duration. While there, the target has the Incapacitated condition. At the end of each of its turns, the target can repeat the save, ending the Spell on itself on a success. It makes the first three saving throws in the demiplane with Disadvantage, ignoring any Magic Resistance for these saves. When the Spell ends on the target, it reappears in a random unoccupied space within 20 feet of the space it left, as determined by the DM.

A target native to another plane of existence doesn't return if the spell lasts for 1 minute. The target is instead transported to a random location on a plane associated with its creature Type.

Using a Higher-Level Spell Slot. You can target one additional creature for each slot level above 4. When you cast this spell using a level 7+ spell slot, a banished target makes all saving throws in the demiplane with Disadvantage.

Rule Tips

• Creature types not affected by this spell: Humanoids, Beasts, Constructs, Dragons, Giants, Oozes, and Plants.
• In effect, if using a level 7+ spell slot, a creature with Magic Resistance has neither Advantage or Disadvantage starting with its fourth save in the demiplane.

Dispel Evil and Good (5th-level Abjuration)

Action: Touch one creature that is Charmed, Frightened, or Possessed by a Celestial, Elemental, Fey, Fiend, or Undead. The creature is no longer Charmed, Frightened, or Possessed.

Dispel Evil - optional rule for grittier possession 

The possessing entity must succeed on a Charisma Saving Throw vs the caster’s Spell Save DC. On a critical success (natural 20 on the save), the spell fails. On a successful save, the effects of the Possessed condition are suppressed for 24 hours. On a failed save, the effects of the Possessed condition are suppressed for 7 days. On a critical failure (natural 1 on the save), the Possessed condition ends and the creature is banished back to its home plane.  

If the possessor is a legendary creature, it can expend one use of its Legendary Resistance feature to obtain a critical success. 

Exorcism ritual 

1-hour Dispel Evil ritual for Exorcists

Casting Time: 1 hour (requires Concentration) 
Requirements: You must be within 15 feet of the Bound or Restrained target for the full duration.

Participants: Up to Proficiency Bonus additional creatures (must be non-Evil, sentient, and able to speak).
Each participant grants +1 to your Constitution Saving Throws to maintain Concentration during the ritual.
Participants are encouraged to be protected by a Magic Circle or Hallow spell, and to wear the holy symbol of a Good deity for a +2 bonus to their mental saving throws (INT, WIS, CHA).

Manifestations:

• The entity may speak, taunt, swear, physically distort the host, use its Horrific Visage action (see below), or attempt to break free from bounds. 
• The entity might be able to use some of its abilities from its normal stat block (DM adjudication). 
• At 15 minutes and 30 minutes into the ritual, participants must make a DC 13 Wisdom Saving Throw or take 2d6 Psychic Damage and gain 1 Exhaustion level. If this damage reduces a participant to 0 Hit Points, they drop to 1 HP instead.

Horrific Visage (Action)

Each creature in a 60-foot Cone that can see the Possessed creature and isn’t Undead must succeed on a DC 13 Wisdom Saving Throw or take 2d6 + 3 Psychic or Necrotic Damage (DM's choice) and gain the Incapaciated Condition until the start of the possessor’s next turn.

On a success, the creature is Immune to this possessor’s Horrific Visage for 24 hours.

Final Saving Throw:
At the end of the Ritual, the possessing entity makes a Wisdom or Charisma Saving Throw (entity’s choice) against the caster’s Spell Save DC.

• +1 to DC per additional participant.
• Disadvantage on the save if the Possessed creature is inside a Magic Circle (spell) and there is a Good-aligned Cleric or Paladin as a participant. 

Outcomes:

• Failure: The entity is expelled into an unoccupied space within 15 feet. Combat may ensue. The host's Corruption score decreases by 3, and it is Immune to Possession by that entity for 7 days.
• Failure by 5+: The entity is banished to its home plane, but not without Screaming first as a Reaction (30 ft. Radius, DC 13 Constitution saving throw or take 3d6 Thunder damage). 
• Success: The ritual fails; the host retains its Possessed condition.

Exorcist Feat

Prerequisite: Level 8+, Intelligence or Wisdom 13+

Your knowledge of religion, fiends, and rituals allow you to perform exorcisms.

Ability Score Increase. Increase your Intelligence, Wisdom, or Charisma score by 1, to a maximum of 20.

Demonologist. You have Advantage on Intelligence (Religion) checks regarding Fiends, the Lower Planes, and incorporeal Undead.

Exorcism Magic. You always have the Banishment and Dispel Evil and Good spells prepared. You can cast each of these spells without expending a spell slot. Once you cast either spell in this way, you can't cast that spell in this way again until you finish a Long Rest. The Dispel Evil and Good spell has the Ritual tag for you. The spells' spellcasting ability is the ability increased by this feat.