Demon Cult Domain

Some Clerics are devoted priests that cure men and women for free throughout the land. Some preach in the name of their holy Gods. Others sacrifice babies to demons.
Clerics of the Demon Cult are distant, disturbed and dangerous members of society. Most societies would shun them on sight. That's why most Demon Cult Clerics keep their lifestyle hidden in plain sight. They worship Demons and, depending on the type of the demon, they make sacrifices to gain otherworldly powers.

Blessing of the Wicked

At 1st level, you know Abyssal and gain proficiency in the Religion skill. Whenever you make a Religion check regarding demons, you double your proficiency bonus for that check.

Scent of Death

Also at 1st level, after you roll for Initiative, your damage and healing rolls increase by 1 (maximum your proficiency bonus) for every creature that is reduced to 0 hit points during the encounter within 120 feet of you. After the encounter is over, you lose these bonuses.

Channel Divinity: Summon Demonoids

Starting at 2nd level, you can use your Channel Divinity to summon demonoids that disrupt your enemies.
As an action, you stab yourself with your holy symbol suffering 1d4 piercing damage. Demonoids are gathered around by the smell of your blood. You designate a target within 120 feet of you. The Demonoids do their best to mess with the target. Consult the Demonoid Effects table below to determine which effect takes place at the start of each of your turns based on the damage you suffered. The Demonoids remain on the target for one minute and have an AC of 10 + your proficiency bonus and 5 + your Wisdom modifier hit points. They are considered a Swarm. If they die, the effects of your Channel Divinity end.

Demonoid Effects Table

1-target has disadvantage on attack rolls

2-target's ac drops by 1d4

3-target suffers 1d6 piercing damage

4-attacks against target have advantage

Decaying Magic

At 6th level, when a cantrip or a spell of yours damages a creature, you can use your bonus action to half their feet of movement until the end of their next turn.

Desecrated Ground

At 8th level, you can desecrate a 30-foot radius area around you. The process takes up to 1 hour and you need to be Concentrating on it. Creatures within the area are immune to radiant damage. Additionally, Demonoids in the area from the Summon Demonoids Channel Divinity, have 2 effects instead of 1. You suffer 1d4 damage again to determine
the extra effect. If you roll the same effect twice, reroll unless the effect stacks naturally like the 2nd and 3rd effect.
You can use Desecrated Ground once per long rest.

Demonic Litany

At level 17, you can use up your entire turn to summon a CR 7 Demon at the start of your next turn. To begin summoning the Demon, you must not move, use an action, a bonus action or a reaction until the start of your next turn. The Demon is uncontrollable by you but will aid you and your allies in battle as the DM sees fit. In the presence of a Demon from the Demonic Litany, Demonoids from the Summon Demonoids Channel Divinity cause all four effects every turn.
You can use Demonic Litany once per long rest.