Cult Domain

Cult Domain Spells
Cleric Level            Spells
1st                           Burning Hands, Ice Knife 
3rd                          Flaming Sphere, Snilloc's Snowball Swarm 
5th                          Fireball, Sleet Storm 
7th                          Ice Storm, Wall of Fire 
9th                          Cone of Cold, Immolation 

Fiend Worship

At 1st level, when you choose this domain, you choose a fiend cult to worship and gain its feature. You must make or acquire a physical object - an amulet or similar adornment - that incorporates some symbols of the path you choose. At your option, you also gain minor physical attributes that are reminiscent of your fiend worship. For example, darkening or reddening of the skin, changes in eye color or protrusions from the body. Once you choose a fiend Worship you cannot change it later.

Devil. You are resistant to fire damage and gain Devil's Sight. Magical darkness doesn't impede your darkvision. You can also speak, read and write in Infernal.

Demon. You are resistant to cold damage and gain Magic Weapons. Your weapon attacks are considered magical. You can also speak, read, and write in Abyssal.

Presence of Fiends

At 1st level, you gain the ability to occasionally sense the presence of fiends. As an action, you can open your awareness to magically detect fiends. Until the end of your next turn, you know the location of any fiend within 60 feet of you that isn't behind total cover and that isn't protected from divination magic. This sense doesn't tell you anything about a creature's capabilities or identity.

You can use this feature a number of times equal to your Wisdom modifier (minimum of once). You regain all expended uses when you finish a long rest.

Channel Divinity: Cult Minion 

Starting at 2nd level, you can use your Channel Divinity to call forth and summon a minion that you have control over. This minion listens to your commands. If your minion dies and you summon another it is never the same one.

Devil. You summon a Imp minion for up to 8 hours in an unoccupied space within 30ft of you.

Demon. You summon a Quasit minion for up to 8 hours in an unoccupied space within 30ft of you.

Fiendish Resilience 

At 6th level, you gain the ability to impede the elements and bathe in their effects. As a reaction when an ally that you can see within 30 feet of you suffers from a damage type based on your Cult Worship, you take half of the damage they would take. 
Devil. Fire damage
Demon. Cold Damage

You can use this feature a number of times equal to your Wisdom modifier (minimum of once). You regain all expended uses when you finish a long rest.

Fiend Strike

At 8th level, you gain the ability to infuse your weapon strikes with fiendish energy. Once on each of your turns when you hit a creature with a weapon attack, you can cause the attack to deal an extra 1d8 damage based on your Cult Worship. When you reach 14th level, the extra damage increases to 2d8.
Devil. You deal fire damage.
Demon. You deal cold damage.

Otherworldly Weapons

At 17th level, your cult worship of the fiend has become strong enough to bestow power and benefits to you. You gain benefits based on your Cult Worship.

Devil. You gain Infernal Wounds. Once per turn when you hit a creature with a weapon attack, if the target is a creature other than an Undead or a Construct, it must succeed on a Constitution saving throw or lose 5 (1d10) Hit Points at the start of each of its turns due to an Infernal wound. Each time you hit the wounded target with this Attack, the damage dealt by the wound increases by 5 (1d10). Any creature can take an action to stanch the wound with a successful (Wisdom) Medicine check against your save DC. The wound also closes if the target receives magical Healing.

Demon. You gain Demonic Weapon. When you hit with a weapon attack, if the target has at least one head and you rolled a 20 on the attack roll, the target is decapitated and dies if it can't survive without that head. A target is immune to this effect if it takes none of the damage, has legendary actions, or is Huge or larger. Such a creature takes an extra 6d8 slashing damage from the hit.