Plague Doctor Domain

These clerics have devoted themselves to eradicating diseases & curing poisons. However, as they say the poison is in the dose and you know just how to tailor your magical doses oto kill or save.

Domain Spells

Spell Level	Spells
1st	detect poison and disease, poison spray, ray of sickness
2nd	lesser restoration, ray of enfeeblement
3rd	revivify, stinking cloud
4th	blight, death ward
5th	cloudkill, contagion

Plague Doctor's Tools

When you choose this domain at 1st level, your study in medicine and disease has given you proficiency in several tools and practices. You gain proficiency in both Poisoner's and Herbalism Kits. Additionally you gain proficiency in the Medicine skill if you don't already have it.

Inoculation

Also starting at 1st level, your constant exposure to different diseases and poisons has has bolstered your immune system to incredible levels, and you've learned how to temporarily share part of this ability with others. You gain resistance to poison damage and you gain advantage on saves vs being poisoned. Additionally you are immune to disease.

As an action you can touch one willing creature and give them resistance to poison damage and advantage on saves against being poisoned for up to 10 minutes. Once you use this ability you can not do so again until you complete long rest, or you spend a spell slot of any level to use it again.

The Dosage makes the Poison

Finally, when you cast a healing spell of 1st level or higher that targets at least one creature, and requires a die roll, you can choose to instead of healing the target deal poison damage equal to 2X the amount they would have been healed for. When you attempt this the target(s) get to make a constitution saving throw against your spellcasting DC. If they Succeed they take no damage.

Channel Divinity: Sickening Presence

Starting at 2nd level, you can use your Channel Divinity to spread sickness to those around you.

As an action, you present your holy symbol and evoke a sickening energy. Each creature of your choice within 20 feet of you must make a constitution saving throw. If they succeed this effect ends, but if they fail they are poisoned until the end of your next turn.

The range of this effect increases to 30 feet at cleric level 17.

Custom Poisons

Beginning at 6th level, whenever yo make a check using your medicine skill, poisoner's kits, or herbalism kits you can double your proficiency bonus for checks made using them, provided you aren't already benefiting from a similar effect.

Additionally when you cast a spell or use a channel divinity that requires a saving throw to avoid the poisoned condition or to avoid/reduce poison damage, you can choose a number of creature in the area, up to your wisdom modifier, and have them automatically succeed on their save.

Divine Strike

At 8th level, you gain the ability to infuse your weapon strikes with divine 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 poison damage to the target. When you reach 14th level, the extra damage increases to 2d8.

Aggravate Poison

At 17th level, as a bonus action you can deal 3D10 poison damage to each creature of your choice within 30ft of you that has the poisoned condition. 

Mithridatism

Starting at 17th level, you gain immunity to poison damage and the poisoned condition.