Pact of the Sludge

Oozes don't scheme, oozes don't hate, they are usually obstacles that adventurers don't give much notice. However, if left alone for long enough, there's a slim chance an ooze will be able to keep eating and growing in the dark, dank corners that go ignored for decades, maybe even centuries. A portion of these gluttonous globs will in time slowly recognize patterns, interpret the behaviour of prey and even create rudimentary plans. The first steps towards sentience have begun. With enough time and prey, a few hundred of these oozes have gained a powerful sense of intelligence and arcane intellect. They find a new method of growing by reaching out to others and offering power if they assimilate food on their behalf. What begins as a simple transaction eventually spirals into a morbid relationship as the warlock's body becomes indistinguishable with the ooze it serves. The urge to join it's patron as part of the collective will inevitably grow too great over the years, and succumbing to this urge is the fate of all but the most willful of Sludge Warlocks.

The patrons of Sludge Warlocks are either Jubilex, powerful Oblex elders or lesser oozes that have grown in power as described in the last paragraph.

Sludge Warlocks are one of the most disgusting people one could meet. With help from their patron, they have learned to use their inner resilience to cast spells. Sludge Warlocks cast spells using their Constitution modifier, rather than their Charisma modifier.

Expanded Spell List

The Sludge lets you choose from an expanded list of spells when you learn a warlock spell. The following spells are added to the warlock spell list for you:

 

1st Level:  Acid Stream,  Grease.

2nd Level: Find Traps, Web.

3rd Level: Meld into Stone, Wall of Water

4th Level: Vitriolic Sphere,  Freedom of Movement.

5th Level: Reincarnate,  Cloudkill.

Glop Guard

Your initial pact begins the bonding process between you and your patron. As such you gain a thick layer of slime on your person at all times. The slime is the same colour, smell and consistency of that of your patron. This layer can be dismissed for up to an hour, but after that the layer will manifest over the course of ten minutes. The layer can only be dismissed once per long rest. After all, your patron is a part of you now, and you cannot fully detach yourself from it. While manifested on your person, the layer has the following effect:

If you aren't wearing armor, your base AC becomes 13 + your Constitution modifier. The spell ends if the target dons armor or if you dismiss the slime as an action. As the slime weighs on your person, you cannot use your Dexterity modifier to calculate AC while you are covered in the slime layer.

The disgusting nature of the Glop Guard imposes a -3 penalty to all Charisma rolls.

Ooze Attachment

Your Glop Guard can no longer be dismissed. It has sunken deep into your pores and into your very bones. As such the boon of the ooze that has been gifted to you can be wielded with greater ease, affording you new benefits:

Resistance to acid and nonmagical slashing, bludgeoning and piercing damage.

Advantage against charm and frighten effects.

A vulnerability towards either fire or cold damage. You choose when you take this feature.

Mutually Mucky

At this point it's hard for a Sludge Warlock to remember what it is like to have a fully solid body. They have an uncanny ability to weave their forms from their humanoid body to that of their Ooze patron. When unarmored, they gain the following benefits:

A climbing speed equal to half your walking speed. You can climb on ceilings if not over-encumbered.

Your unarmed attack is replaced with an acidic pseudopod that deals 1d6 + Strength modifier in acid damage.

Mucus Master

At this point your bond to the patron is total. You think on their terms as well as your own. It is at this time that Sludge Warlocks tend to begin to feel the urge to merge with their patron, and can concentrate in order to gain a very broad sense of what direction their patron is in. They gain a benefit that depends on the kind of Ooze their patron is:

Black Pudding & Grey Ooze: A creature that touches you or hits you with a melee attack while within 5 feet of you takes 1d6 acid damage. Any nonmagical weapon or armor made of metal or wood that hits the pudding corrodes. After dealing damage, the weapon takes a permanent and cumulative -1 penalty to damage rolls. If its penalty drops to -5, the weapon or armor is destroyed. Nonmagical ammunition made of metal or wood that hits you is destroyed after dealing damage.

Elder Oblex: The Sludge Warlock gains an appetite for memories from their master. Once per short rest you may target a creature within 5ft. They must make a Wisdom saving throw (DC = 10 + Constitution modifier) or be memory drained until it finishes a short or long rest or until it benefits from the restoration or heal spell. Constructs, oozes, plants, and undead succeed on the save automatically.. While memory drained, the target must roll a d8 and subtract the number rolled from any ability check or attack roll it makes.  

Gelatinous Cube: Once per short rest, you can grow to take up exactly 10ft by 10ft for 5 rounds. While in this form you can engulf one creature of Large or smaller size. When performing this action the target must succeed on a Dexterity save (DC = 10 + Constitution modifier). On a failed save, you enter the creature's space, and the creature takes 3d6 acid damage and is engulfed. The engulfed creature can't breathe, is restrained, and takes 21 (6d6) acid damage at the start of each of the cube's turns. When the cube moves, the engulfed creature moves with it. An engulfed creature can try to escape by taking an action to make a Strength check (DC = 10 + Constitution modifier). On a success, the creature escapes and enters a space of its choice within 5 feet of the cube. An engulfed creature does not count as grappled.

Jubiliex: The Warlock's blood flows with the eternal foul ichor of the demon prince. You regenerate hit points equal to 1d6 at the start of each of your turns.  If it takes fire or radiant damage, this trait doesn't function until you take a long rest. This ability reacts to feelings of danger, and only functions during combat.

Slithering Tracker: This patron is deeply attached to the blood of mortals, and it's servants share this understanding. Your unnarmed attacks deal and extra 2d6 necrotic damage.