The Vermin Lord

The farmer curses the name of the locust, the tavernkeeper curses the name of the rat, and the potion-maker curses the name of the stink-worm just as society curses yours. You have been tossed aside my the masses, left to find solace with the rest of the misfits and unwanted critters. Your presence is hardly acceptable at a squalid bar, let along walking the streets. Your life is such that it would be a benefit for you to meet your end, but still you cling to your existence. So you sulk through life, hiding away from humanity and getting to know your friends who creep and crawl alongside you.

Although Warlocks have high Charisma, worshippers of the Vermin Lord display how having high Charisma doesn't always mean that everybody likes you. This subclass is a challenge to roleplay well, because of this contradiction. I suggest playing a manipulative, cruel little monster, but that's up to you, man. Usually Vermin Lord worshippers don't worships actual gods of vermin, but rather a god of a related field (such as death or famine), and then put their own little twist on things. Sometimes, however, they do actually worship gods like the Great Horned Rat or someone like that.

Exploit the Servants

You can cast 'animal friendship,' 'speak with animals,' and 'animal messenger' at will on any Tiny rodent or insect. Additionally, you can consume a Tiny rodent and regain 1 HP as an action.

Spew Vermin

You spew locusts in a 15ft cone. All creatures in this area must make a Dex. save (Spellcasting DC). If they fail, they take 5d6 (17) piercing damage. On success, half damage. The targets also take poison damage equal to the amount of piercing damage they took. You gain temporary HP equal to the amount of poison damage taken by the target who took the most poison damage. The locusts do not count as creatures, but rather as a side effect of this ability and can therefore not be used as allies. You must take a long rest before using this ability again.

Plague Carrier

Once per long rest, you can cast the spell 'Contagion' without expending a spell slot. When you cast the spell this way, the target has disadvantage on their Con. saves while within 15ft of you.

Rat Pack

As a bonus action, you can transform into a Swarm of Rats. You can stay in this form for up to an hour, after which you transform back. If the rat pack is separated after an hour, each rat transforms into a proportionate chunk of your flesh and you die instantly. If rats in the the rat pack die, they do not transform back when you do. Instead, they dissolve as soon as they die. If all the rats die, the last rat turns into your whole body immediately upon its death. For additional rules on this transformation, it is identical to a Druids' Wild Shape. You can make this transformation an amount of times equal to your Charisma modifier per long rest.