Exorcist

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

• Increase your Intelligence or Wisdom score by 1, up to a maximum of 20.
• You have advantage on Intelligence (Religion) checks related to fiends and fiendish planes of existence.
• You can create (acolyte background, clerics, paladins, cleric magic initiate feat), or obtain holy water at half the normal cost. 
• You can perform minor and greater exorcisms; see below.

MINOR EXORCISM

You can spend an action praying or meditating in the presence of fiends or undead and gain the benefits of the Bless spell for a maximum of 1 minute, during which time you  gain resistance to necrotic damage. To keep these benefits active, you must use your "free" utterance on your turn to pray/meditate aloud. If you cast a spell or cease to pray, you lose the benefits. You can use this feature once per long rest.

GREATER EXORCISM

As a 1 hour ritual, you can attempt to send a fiend back to its native plane of existence. This may be attempted on a possessed creature. The fiend or possessed creature-- preferably bound (paralyzed) or restrained-- must be within 15 feet of you during the entire ritual. If performed on someone afflicted with demonic possession, the demon takes total and precise control of the creature during the ritual. The fiend can physically manifest itself during the ritual, distorting or replacing the possessed creature's normal form. The fiend can attempt to break the bonds to fight the exorcist and its allies. (Ideally, participants are protected by a magic circle spell). If the possessed creature takes damage at any time during the ritual, it can make a DC 20 Wisdom saving throw. On a success, it takes back control of its body and the ritual fails. The ritual also fails if the possessed creature escapes or you become incapacitated. 

15 minutes into the ritual,  participating creatures or those observing the scene must succeed on a DC 12 Wisdom saving throw or become frightened. You have advantage on this save. Those that succeed on the save benefit from the effects of a Protection from Evil and Good spell for the rest of the ritual's duration. 

Once the 1-hour ritual is complete, make a DC 20 Intelligence (Religion) check. The check is made with advantage if you also have proficiency in the Intimidation skill or if you are assisted in the ritual by a devoted cleric or paladin. On a success, the target is banished with a faint popping noise, returning to its home plane. On a failure, the target isn't banished and you gain 1 level of exhaustion. 

If the target is native to the plane of existence you're on, you banish the target to a harmless demiplane. While there, the target is incapacitated. The target remains there for 24 hours, at which point the target reappears in the space it left or in the nearest unoccupied space if that space is occupied. If you performed the ritual on a possessed creature, the fiend doesn't repossess that creature when it reappears. 

A banished fiend with a challenge rating of 4 or higher can make a DC 20 Charisma saving throw every 24 hours. On a success, it can choose to reappear somewhere on the plane of existence you're on.  

Whether it succeeded or failed, you can't perform the ritual again until you complete a long rest. 

Homebrew feat