The Great Ooze

There is something strange about the minds of the great oozes. They are as unknowable as any great being, and yet also simpler than a beast in some regards. Their power is undeniable, but their form is perhaps unusual, even among demons, devils and other outsiders. Great oozes occasionally will offer a mote of their power to a warlock, however, and then things get truly strange.

Also you're supposed to get Tasha's caustic brew and Evard's Black Tentacles but I don't have the rights to those so I couldn't include them, do with that information what you will.

Protean form

Beginning when you take this archetype at 1st level, the ooze has provided you with the power to temporarily melt your form into a mass of slime to travel through obstacles. You have resistance to acid damage. Additionally, over the course of your movement, you may travel through gaps as narrow as 1 inch wide, including through spaces occupied by enemies. Difficult terrain also does not slow your movement speed.

Also, you can perform grapple checks using your Constitution modifier rather than your Strength modifier, and targets you are grappling have disadvantage on attacks against you.

Slime Invasion

Also at 1st level, you can ride inside targets to shield yourself from harm. As a bonus action, you can ride inside an allied creature adjacent to you or attempt to force yourself inside of an enemy you are grappling. An enemy must make a Strength saving throw against your spell save DC to avoid swallowing you. A creature with no mouth or that otherwise cannot eat automatically succeeds this saving throw. While swallowed in this way, the following effects are active, affecting both you and the creature:

• You Can't take any Actions or Reactions except those allowed by these effects.
• You fill the creature's stomach capacity, including an Eating check for overindulging. Creatures with no maximum stomach capacity treat your size in their stomach as double your normal weight. You are not food, however, and thus you cannot be digested or affected by spells like Abyssal Stomach
• You have total cover from any effects not originating inside your target. You do however also take any falling or thunder damage the target suffers.
• You can use your bonus action to overfill your target, increasing your volume in their stomach by a number of pounds equal to your Proficiency bonus.
• You can use your reaction whenever your target would be forced to eat food to consume any food they ingest until the start of your next turn, adding it to your stomach capacity instead of theirs.
• Your target can use their Action to attempt to expel you, making a Strength Saving throw against your spell save DC. On a failure, they cannot repeat the action again until after their next turn. On a success, you leave their body and the effects of this feature end.
• An allied creature can allow you to use them as a focus for spellcasting, allowing you to cast spells as normal, originating from them and using their line of sight for determining effects.
• You can use your Action to force an enemy creature to make an attack with one of its weapons against another creature within its range.

These effects last until the creature dies, at which point you are ejected from them and emerge in an unoccupied space within 5 feet, or until you choose to leave them as a bonus action on your turn.

Splattering Escape

Beginning at 6th level, whenever you take a hit, you can splatter yourself across the area in response, spraying creatures with acid before reforming yourself somewhere safer. When you take damage, you can use your reaction to splatter yourself, turning into a spray of ooze that causes each creature within 10 feet of you to take 3d6 Acid damage. You are no longer a creature for this duration, and you reform in a location within 30 feet at the start of your next turn, the ooze seeping into that location to reshape into your form.

Once you use this feature, you can’t use it again until you finish a short or long rest.

Improved Protean Form

At 10th level, the malleability of your form improves, granting you greater control. You can Disengage as a bonus action. When you do, you can attempt to use your Slime Invasion on an enemy creature within your movement range by moving into their space. When you do this, you force them to make a Dexterity Saving throw rather than a Strength saving throw, but they then suffer the effects as normal on a failure.

Additionally, your resistance to acid damage becomes immunity.

Slime Mastery

At 14th level, your Slime Invasion improves, allowing you to add any or all of the following effects of your choice while using it.

• The target is immobilized. If they have no bulk limit, increase their weight by 4 times their current weight.
• The target is affected by the Enlarge portion of Enlarge/Reduce
• The target cannot speak, simply dribbling slime whenever they attempt to.
• You can use your bonus action to force the target to move up to their movement speed in a direction of your choice, ignoring any movement speed penalties from their weight.
• You can use your bonus action to force an enemy target to let you use them as a focus as if they were an allied creature until the end of your turn. They must make a Charisma saving throw against your Spell Save DC, preventing you from doing this on a success.
• You can grant an Allied target any damage resistances or immunities you also possess.