The Pestilent One Patron

You have made a pact with a sickening pestilence. An infectious entity who spreads diseases and sires vermin that allows you to draw from its plagubearing magics. 

Maybe you were born sick and made a pact with the pestilent one for few more years, and now you have to make others ridden with disease. Or maybe you are a doctor, who studies pathogens and made a pact for knowledge, and now have to profuce your own specimen as payment for your power.

Pestilent Spells

At 3rd level when you gain this subclass you learn extra spells. You learn additional spells when you reach certain levels in this class, as shown on the Pestilent Spells table. Each of these spells counts as a warlock spell for you, but it doesn’t count against the number of warlock spells you know.

 

Pestilent Spells Table:

3lvl	bane, ray of sickness, ray of enfeeblement, blindness/deafness
5lvl	Bestow Curse, Stinking Cloud
7lvl	Blight, Confusion
9lvl	Cloud Kill, Contagion

Tide of Vermin

At 3rd level you gain the ability to summon a verminswarm to aid you. As an action or whenever you subject a creature to successfully have the poisoned condition, you can summon a verminswarm that uses the stat block of swarm of rats in a space you can see within 30 ft from you for 10minutes. At 6th level you can summon a number of swarms up to your proficiency bonus. 

If your proficiency bonus is higher than the verminswarms, the swarm uses yours instead of its own, the verminswarm uses your spell attack modifier for its attack modifier. The swarms share your initiative count. You can issue telepathic commands to all your summoned swarms as a bonus action. If a command has not been issued, the swarms take the dodge action. The vermin swarm can communicate simple ideas to you telepathically in 300ft radius from you, and understand you.

You can use this feature a number of times equal to you proficiency bonus + Charisma Modifier. Regaining spent uses on a long rest.

Plague Spreader

Also at 3rd level you can start to spread infections when you strike your enemies. Once a turn when you hit a creature with an attack roll or a verminswarm hits a creature with their bite attack, you can turn the damage type into poison damage, deal an extra 1d6 damage. The creature must make a CON save against your spell save DC, or gain the poisoned condition until the start of your next turn. At 6th level, your swarms can use this feature at will.

Herald of pestilence

At 6th level your tether to all things infectious have granted you resistances to your craft. You gain immunity to the poisoned condition and resistance to poison damage.

Also you can cast Stinking Cloud as a bonus action, without using a spell slot once per short rest. At 10th level when you cast Stinking Cloud this way, it does not require concentration.

Feverish infection

At 10th level your infections start to spread easier. When you or verminswarm subjects a creature to make a saving throw against the poisoned condition, the creature makes their save at disadvantage.

Also when verminswarm dies, each creature in 5ft radius from it must make DEX save, or take 2d6 poison damage and gain the poisoned condition until the end of their next turn. Taking half damage on a successful save.

Rotlords Scourge

At 14th level your infections grow in their severity. When a creature gains the poisoned condition a third time or more in a minute from you and/or a verminswarm, they gain a natural disease at random by rolling 1d6 that last for 7 days:

• 1 : Blinding Sickness: Pain grips the creature's mind, and its eyes turn milky white. The creature has disadvantage on Wisdom checks and Wisdom saving throws and is blinded.
• 2 : Filth Fever: A raging fever sweeps through the creature's body. The creature has disadvantage on Strength checks, Strength saving throws, and attack rolls that use Strength. The creature can only use of its turn actions (action, bonus action, reaction, movement) in a turn or it takes a point of exhaustion.
• 3 Flesh Rot: The creature's flesh decays. The creature has disadvantage on Charisma checks and vulnerability to all damage.
• 4 Mindfire: The creature's mind becomes feverish. The creature has disadvantage on Intelligence checks and Intelligence saving throws, and the creature behaves as if under the effects of the confusion spell during combat.
• 5 Seizure: The creature is overcome with shaking. The creature has disadvantage on Dexterity checks, Dexterity saving throws, and attack rolls that use Dexterity, and also moves at half speed.
• 6 Slimy Doom: The creature begins to bleed uncontrollably. The creature has disadvantage on Constitution checks and Constitution saving throws. In addition, whenever the creature takes damage, it is stunned until the end of its next turn.