When an ooze has lived for enough time and has accumulated enough material, it becomes so large and heavy that it cannot hunt anymore. Thus, it undergoes a metamorphosis, anchoring itself to a location and creating a lair. From there, it sheds parts of it into new, mobile oozes, who after hunting for prey return and re-assimilate to the primary “body” to provide nutrition. These ooze “colonies” constantly expand, spreading further and further away from the anchoring point as food sources get depleted and prey flees. If left unchecked, these infestations can grow to absurd size, claiming entire territories. While thankfully such dangers are noticed quickly at the surface, it is rumored that deep underground, massive ooze organisms stretch across hundreds of kilometers, slowly but inexorably carving out their own “kingdom”.
Mechanics (DnD 5e)
Due to its nature, a primordial ooze isn’t really a creature in terms of mechanics, but more of a territorial effect. Designate an area that belongs to the ooze. This can range from a small cave to a ruined castle to a massive tunnel network. Oozes within this territory gain the following benefits:
- Any ooze gains a +1 bonus to attack and damage rolls.
- Any ooze increases their speed by 5 feet.
- When a Black Pudding or Ochre Jelly split, the two new oozes gain 1d6 temporary hit points.
- When a Gelatinous Cube attempts to engulf a creature, the DC of the Dexterity saving throw to avoid it increases to 14. It also gains the following reaction: Recharge 6: When an engulfed creature attempts to escape the cube, it can use a reaction to impose disadvantage on the roll. If the cube does so, it cannot move until the end of its next turn.
- Gray Oozes gain the Split reaction that Black Puddings and Ochre Jellies have.
The primordial ooze has no AC or abilities. However, it has a pool of hit points, that are expended to create mundane forms of oozes. A brand new anchored primordial ooze would have a bit over 200 HP, but ancient ones could reach well into the thousands, able to summon a true army. To give some idea about the numbers, a Black Pudding has 85 (10d10+30) HP, a Gelatinous Cube has 84 (8d10+40), a Gray Ooze has 22 (3d8+9) and an Ochre Jelly has 45 (6d10+12)
In order to kill such a creature, you would simply have to make it summon more and more mundane oozes to defend itself, until it eventually ran out of HP to use. You could limit the number of oozes summoned each turn either with a hard number, or a percentage of the primordial’s total or remaining HP.
You could also make the area more dangerous with the following effects:
- Any non-ooze creature within the area takes 1 acid damage at the beginning of each of their turns.
- After each hour spent in the area, any nonmagical metallic equipment corrodes as if affected by a Black Pudding’s Corrosive Form or Pseudopod.
- Whenever an ooze dies within the area, other oozes within 10 feet of it absorb its remains, regaining 1d4 hit points (one roll for all oozes).
By adjusting the total pool of HP the primordial ooze has available, you can tweak the difficulty of the encounter according to your will. As you can guess though, I don’t advise you to convert the primordial into an ooze mob in one go – the fight should be done in waves in order to not overwhelm the players.
And since I apparently neglected to say this before, Oozes are at page 240 of the Monster Manual.
Thanks for reading, and have fun!