Too Much of a Good Thing (A Monster for King of Kings)

The alchemists of the First City, capital of the Enlightened Empire, have isolated the components of air. A foolish endeavor in the eyes of just about everyone else, nobody trusts them when they talk about such abstract notions as "oxygen" and "nitrogen", though there are rumors that agents in service of the Gnostic Elves are seeking out such treatises. It is common knowledge that air is simply a firmament through which the light of the holy blessed God travels. The alchemists are surely wrong.

In the antediluvian days, when the Sea Tyrants held sway over the whole of the world, they would poison the air and the water through mysterious means. Even to this day, there are patches of earth strangled by forgotten machinations, with no plant life clinging to the skeletal dusty dirt. Only the most learned scholars are aware of this fact and who did it.

Nobody knows how.

Oxygenator

Armor Class: 8

Hit Dice: 10 hp (mobile form) or 30 hp (sessile form)

Attacks: see below

To-Hit: N/A

Movement: 12' (4')

Saving Throws: D8/W9/P10/B10/S12

Morale: 12

Alignment: Neutral

XP: 100

Number Appearing: 2d6 (in mobile form unless otherwise specified)

Damage Resistance: Oxygenators take half damage from all bludgeoning weapons and all non-magical slashing and stabbing weapons.

Damage Weakness: Oxygenators take double damage from fire. They are weak to certain salves and rubs.

Hyperoxia: Oxygenators produce excessive amounts of oxygen, causing oxygen poisoning. Oxygen poisoning only begins to take effect if the oxygenators are in a small contained area or in direct contact with an air-breathing subject. For every turn (when in a contained space) or every round (when in direct contact), make a save vs. poison. Track how many failed saves have been made by each air-breathing subject in the area:

1: nausea and confusion (-1 to all rolls (incl. saves))

2: tunnel vision (-1 to attack rolls (-2 including the above penalty) and AC)

3: drowsiness (-1 to all rolls (incl. saves))

4: convulsions (disadvantage on attack rolls, half movement)

5: uncontrollable vomiting (cannot take any actions other than moving)

6: fall unconscious

7: amnesia (lose a level)

8: instant death

Mobility: Oxygenators can alternate between a slow oozelike mobile form and a sessile form in the appearance of a lumpy column. They cannot move when in the sessile form. It has a much lower HP amount in the mobile form, and any damage sustained in mobile form is maintained when it transforms into its sessile state. It will automatically switch to its sessile form if it reaches 2 HP. They are especially dangerous in the mobile form, since they can crawl onto the faces of air-breathing creatures to accelerate the process of hyperoxia.

The mobile form might look more or less like good ol' fashioned green slime (though more mobile so its not just doomed to dripping)

Okay breaking the whole in-character style of the beginning of this post to talk about what this thing actually is. The oxygenator is a colony of oxygenating bacteria held in a matrix of green algae and animated by sea tyrant sorcery. It was developed as a weapon of war during the incessant skirmishing between rival fish lords. Hyperoxia and oxygen poisoning are real conditions that were one of the largest inspirations behind this creature, and the effects of the failed saving throws are based directly on actual symptoms of oxygen poisoning (though usually it takes you longer than 80 minutes to die from it lol). This actually isn't the first time this creature has appeared in my game worlds; The World With No Name, which is the setting that I ran my games in in high school, featured an antediluvian empire of Cambrian overlords who used these bacterial beasts to make areas inhabitable in a nearly oxygen-less world. There are still Cambrian influences on the Sea Tyrants in King of Kings, but they're primarily Devonian and Carboniferous in inspiration, so turned the original purpose behind this thing's creation to one more suitable to the more developed/evolved antediluvian overlords.