Plague Cleric

Of the many gods of the pantheon you chose to the God of Decay, Patron of the Ill. What pushed you to such a gloomy path?

Bonus Proficiency

When you choose this domain at 1st level, you gain proficiency with the use of the Poisoner's Kit, Herbalist Kit and Heavy Armor.

Plague Bearer

As an action you can create a miasma of pestilence around you, enemies within 10 feet of you must make a Constitution Saving Throw against you spell save DC or become violently ill, getting disadvantage on all future attack rolls, skill checks and dexterity saving throws until they succeed. They can repeat the saving throw at the end of their turn until they succeed.

You can use this feature a number of times equal to your wisdom modifier and regain all uses on a long rest.

Channel Divinity: Plague Sense

Starting at 2nd level, you can use you Channel Divinity feature to negate damage to a friendly creatures.

When an ally you can see within 15 feet of you would take damage, you can use your reaction to turn the damage into a heal. If the damage is necrotic you can add you Wisdom Modifier to the heal.

Aura of Decay

Beginning at 6th level, once on each of your turns, when you hit a creature with a melee weapon attack, you can give that creature disadvantage on Constitution Saving Throws until the ends of their next turn.

Plague Weapon

At 8th level, you can attune to a weapon, this weapon becomes a conduit of the foul energies that you command, rusting the steel as pustules grow on the handle and blade, oozing with disease.

Attacks done with your plague weapon deal an additional 1D8 Necrotic Damage. This damage increases to 2D8 at 14th level.

Your plague weapon counts as a magical weapon when overcoming resistances.

Blessed by Pestilence

Starting at 17th level, you've been around so much death, decay and disease that you've become a conduit for them, granting you immunity to diseases and resistance to necrotic damage.

When you finish a long rest, you can grant a number of allies equal to your Wisdom Modifier immunity to diseases and resistance to poison and necrotic damage for 8 hours. Also when you hit an enemy with a melee weapon attack you can use your reaction to automatically inflict one of the following diseases to your target.

Black Decay: A creature afflicted by this disease has they HitPoint maximum reduced by your Cleric level plus your Wisdom Modifier. Each of the following turns this disease is in effect, the creature must succeed a Constitution SAcing Throw equal to your Spell Save DC. On a success theyr health remains the same, on a fail the disease continues to reduce theri HP maximum by your Wisdom Modifier.

Hellish Fever: Creatures affected by this disease has disadvantage on attack rolls and on Wisdom skills and Saving Throws.

Arcanist's Bane: When a creature afflicted by this disease tires to cast a spell, it must roll a Constitution Saving Throw, on a succees the spell is cast a normal, on a failure the spell backfires.
(It's up to the Dm to decide the consecuence based on the spell)

Lethargy: Creatures afflicted with this disease have disadvantage on all Dexterity based skills and Saving Throws and have their speed halved.

All conditions are healed after succeeding three Constitution Saving Throws that are rolles at the end of each of their turns or by a Greater Healing Spell. Natural 20s are treated as two succeses. Diseases do not stack, a new disease replaces the previous one.

Since these are not natural diseases, but the working of a god, immunity to diseases does nothing to stop the effects.