The shambling thing before you resembles a moving pit of tar. As it roils and churns, pulling its indeterminate bulk towards you on foul pseudopods, sharpened points of bone and debris emerge, only to be sucked back into its horrid mass the next second.
You hope the noise it made was just the wind howling through its oddly brittle, porous frame - otherwise, it was a howl of anguish and hatred.
Oozes are a common enough feature of many dungeons. Some live in commensal relationships with other creatures (like humanoids feeding them scraps in exchange for their protection). Some, however, form far more sinister relationships - like the Blackened Ooze.
When an ooze devours Undead, most are simply digested and excreted as with most meals. But, when an ooze eats many such creatures, and lives in an area that is cursed to produce Undead (whether by Divine edict, or perhaps a natural conduit to the Plane of Negative Energy), these horrific creatures can be formed.
Hulking, oily-black beasts, the are tainted with the energies animating the Undead, and end up stuck in some bitter mockery of life - a half-dead state. Their digestive processes begin to shut down, leaving them only just capable of digesting flesh and other organic matter, but little else. The bones and weapons of their kills may break, leaving the surface and innards of the creature filled with razor-sharp spikes and slivers of bone.
Some Necromancers claim knowledge of how to create these foul beasts, and will use them to devastating effect in contained areas.
No. Appearing: 1d2
Size: ~9ft Diameter (Large)
Armor Class: 3
Hit Dice: 6
Attacks: 2 (Slam 2d6, Bashing and Piercing Damage)
Blackened Oozes have an immunity to paralysis, charm and sleep effects. Healing Spells and effects (such as Cure Light Wounds, or a Paladin's Lay on Hands) act as their reversed equivalent (so, Inflict Light Wounds, or Harm for Heal), causing damage instead of healing. Those reversed spells (Harm and Inflict X Wounds) may act as Healing Spells, at the DM's discretion. They can also grapple and overwhelm opponents, who take 1d8 damage per round they are grappled.
One particular Necromancer (whose name has been lost to time) was interested in using these beasts as guardians for her lair, and began to create a large number of them. She also experimented with way to increase their intelligence, to better understand her commands and make for a more effective "watchdog" system. After many years of "breeding" these twisted mockeries of nature, she finally produced a single specimen capable of independent reasoning.
She noticed something strange - unlike other oozes, which split and create a "new" organism, this ooze maintained control over its separated pieces. A quick thought led her to implant a section into a test subject, and lo and behold - the ooze could control the victim, after a fashion. They began to exhibit great sickness, then "died" - only to be raised as a peculiar ooze-filled Undead, totally in thrall to the original. These "Blackened" would form the core of her Undead army, and she terrorised the local populace for many years.
As she researched ways to extend her life, she came to a compromise - she would mentally dominate the ooze, allow it to enter her body, and use magic to stave off it effects - hopefully allowing the symbiont to enhance her body, and extend her lifespan until she could achieve true immortality through Lichdom, or some other Necromantic process.
Sadly (for her), the plan was not to be. She did not realise quite how strong-willed the ooze had become, and instead of infecting her, it simply absorbed her, both bodily and spiritually, into itself - becoming more intelligent, and also quite mad. It had become so accustomed to the Negative Energy that once fed it, it was unable to leave its lair without causing itself great damage, starving itself f those foul energies - but it's working on it. And it may still send its "servants", Undead imbued with its horrid essence, out into the world to do its bidding, and collect the ritual components it thinks it might need to allow it to leave the cold embrace of its home.
Now, this foul creature lurks in the depths of her old lair, under a local dungeon, biding its time until it decides to leave its lair and cause havoc across the land. Locals who have somehow survived encounters with it refer to the creature as "The Creeping Death", a name whispered in the darkest of legends.
The Creeping Death
No. Appearing: 1
Size: ~25ft Diameter (Colossal)
Armor Class: -4
Hit Dice: 12
Attacks: 4 (Slam 2d10, Bashing and Piercing Damage)
Intelligence: High (15)
Alignment: Chaotic Evil
The Creeping Death is a Spellcaster, and may use any Necromancy spells you think it should have. It also shares all immunities with both Undead and Oozes.
When a character is implanted with a lump of the Creeping Death, they must make a Save against Death Magic every hour, or lose one point of Constitution. Once this drops below a quarter of its original score (rounded up), the character begins to show signs of the possession - coughing up black, tarry blood, an unstoppable rage, an inability to feel pain, and a much-toughened physique. Once the character is reduced to 0 Con (or killed normally), they will reanimate within (original Constitution score) minutes, as one of the Blackened. These creatures are totally in thrall to the Creeping Death, and follow its commands without hesitation or error.
No. Appearing: 2d4
Size: Medium (as base creature)
Armor Class: 5
Hit Dice: 2 +5
Attacks: 1 (Slam 1d6) or by weapon
Blackened share all immunities with other Undead creatures (and are, to all intents and purposes, zombies).