Unstable Mutation

Doctor Krizan's Apotheosis

"The tragedy wasn't that Doctor Krizan believed he could create life. It was that, for one impossible moment... he proved he could."

— Professor Helena Laine, Chair of Arcane Ethics, University of Greyhaven

Doctor Edvard Krizan devoted nearly three decades of his life to solving one of the greatest biological mysteries left in the wake of the Sylvan Plague.
While most natural philosophers sought to catalog the countless horrors emerging from the depths of the Iorill Forest, Krizan pursued a far more ambitious goal. He believed the Plague itself possessed an underlying biological logic. Every twisted beast, every grotesque mutation, every impossible organism appeared different on the surface, yet all shared remarkable similarities in their methods of growth, regeneration, and adaptation. To Krizan, these were not random abominations. They were clues.
If those principles could be understood...
Perhaps they could be controlled.
Born in Kestenvale, only a few days' journey from the ancient elven kingdom and the ever-dark reaches of Iorill Forest, Krizan grew up watching caravans return with stories of impossible creatures that ignored conventional anatomy and survived wounds that should have killed anything born of nature. Rangers described predators whose bodies reshaped themselves after injury. Scholars returned carrying fungal colonies that behaved almost like nervous systems. Entire expeditions vanished while investigating organisms that seemed capable of rewriting their own biology.
Most regarded such creatures as nightmares to be destroyed.
Krizan regarded them as unanswered questions.
His earliest work earned widespread respect. He became one of the foremost authorities on Sylvan Plague physiology, publishing meticulous anatomical studies that revolutionized contemporary understanding of the disease. His recommendations for quarantine procedures undoubtedly saved thousands of lives, while his observations concerning regenerative tissue remain standard reading among physicians and natural philosophers alike.
Then his research became increasingly private.
Funding continued.
Publications stopped.
Visitors to Krizan's secluded estate reported seeing heavily guarded supply wagons arriving under cover of darkness, their contents never disclosed. Livestock disappeared from nearby farms with suspicious regularity. Local gravekeepers quietly complained of disturbed burial sites, though no evidence ever proved the accusations directed toward the doctor's household.
Rumors spread quickly.
Some claimed he was breeding infected animals.
Others insisted he had learned to keep Sylvan mutations alive indefinitely.
The most disturbing whispers suggested that condemned criminals had begun disappearing from prisons shortly before scheduled executions.
No investigation ever produced sufficient evidence to justify intervention.
Krizan remained a celebrated scholar.
Brilliant.
Respected.
Increasingly isolated.
Whatever truly occurred within the laboratories beneath his estate remained unknown until the morning everything went silent.
Servants failed to emerge.
Smoke rose from shattered windows.
Neighbors reported hearing sounds throughout the previous night unlike anything they had ever imagined, tremendous impacts, collapsing masonry, and screams that continued long after no human throat should have remained capable of making them.
The first investigators discovered devastation beyond comprehension.
Stone walls had been reduced to rubble from within. Iron restraints thicker than a man's arm had been twisted apart like soft wire. Entire laboratories appeared demolished by something possessing neither restraint nor purpose, as though an avalanche had learned to hate.
Doctor Krizan's body was identified only through fragments of clothing and personal effects recovered beneath the ruins.
The creature responsible had already gone.
No complete notes concerning his final experiment were ever recovered.
What little survived painted only fragments of a terrifying picture. References to accelerated regenerative matrices appeared repeatedly throughout damaged journals. Anatomical sketches depicted muscles continuing to grow despite catastrophic structural failure. Entire pages discussed the possibility of forcing living tissue into perpetual adaptation, allowing wounds to become opportunities for improvement rather than weakness.
The final entries grew increasingly fragmented.
There were repeated references to "stabilization failures."
Then simply...
"It continues changing."
The creature that escaped became known only as the Unstable Mutation.
Whether it represented the culmination of Krizan's life's work or merely another failed prototype has never been determined. Scholars continue to argue whether the doctor sought to create a weapon against the horrors of Iorill Forest, a soldier capable of surviving any battlefield, or a cure for the relentless mutations inflicted by the Sylvan Plague itself.
The answer died with him.
What remains is a living monument to the oldest temptation in every field of science.
The belief that understanding nature entitles one to improve upon it.
Few now question Doctor Krizan's intentions.
By all surviving accounts, he genuinely wished to protect his homeland from the unimaginable horrors lurking beneath the ancient boughs of Iorill.
History remembers him not for those intentions...
But for the single creature that walked out of his laboratory and proved that some discoveries are too dangerous to survive their own success.

"We found the laboratory exactly as the stories claimed. We never found the doctor. Whatever escaped left just enough of him behind to prove he died trying to put it back together."

— Captain Emile Lyon, Kestenvale Shadow Rangers

Genetic Ancestor(s)

• Monstrosity

Scientific Name

mutatio instabilis

Lifespan

3 weeks to 8 years

Average Height

18 to 24 ft.

Average Weight

12 to 20 tons

Average Length

20 to 30 ft.

Geographic Distribution

• Iorill Forest
• Itora

Related Ethnicities

• Kesten

Discovered by

Edvard Krizan

Unknown Shores

Unstable Mutation CR: 16

Huge monstrosity, chaotic neutral

Armor Class: 17

Hit Points: 247 (19d12 + 114) 19d12+114

Speed: 40 ft , climb: 30 ft

STR

27 +8

DEX

10 +0

CON

23 +6

INT

4 -3

WIS

12 +1

CHA

7 -2

Saving Throws: Str +13, Con +11, Wis +6

Skills: Athletics +13, Perception +6

Damage Resistances: bludgeoning, piercing, and slashing from nonmagical attacks

Condition Immunities: charmed, frightened, poisoned

Senses: darkvision 120 ft., passive Perception 16

Languages: understands the languages it knew before its mutation but can't speak

Challenge Rating: 16 ( 15,500 XP)

Proficiency Bonus: +5

Special Abilities

Experimental Organism. The Unstable Mutation doesn’t require air, food, drink, or sleep, and it is immune to disease.
Siege Monster. The Unstable Mutation deals double damage to objects and structures.
Unstable Regeneration. The Unstable Mutation regains 15 hit points at the start of its turn if it has at least 1 hit point. If it takes acid or fire damage, this trait doesn’t function at the start of its next turn.
Mutagenic Instability. At the end of each of its turns, roll a d4. The Unstable Mutation’s body undergoes the corresponding mutation until the end of its next turn.

d4	Mutation
1	Calcified Hide. Jagged plates of bone erupt across its body, granting it a +2 bonus to AC.
2	Elongated Limbs. Its limbs stretch and split. The reach of its melee attacks increases by 5 feet.
3	Overgrown Muscle. Its muscles swell beyond the limits of its frame. Its melee attacks deal an extra 5 (1d10) damage on a hit.
4	Rupturing Tissue. Swollen growths spread across its body. The first time it takes damage before the end of its next turn, each creature within 10 feet of it takes 7 (2d6) necrotic damage.

Relentless Bulk. The Unstable Mutation has advantage on ability checks and saving throws made to resist being grappled, knocked prone, or moved against its will.
Uncontrolled Fury. While the Unstable Mutation has 123 hit points or fewer, its speed increases by 10 feet, and it makes one additional Crushing Fist attack when it uses Multiattack.

Actions

Multiattack. The Unstable Mutation makes three attacks, using Crushing Fist or Mutated Claw in any combination.
Crushing Fist. Melee Weapon Attack: +13 to hit, reach 10 ft., one target.
Hit: 19 (2d10 + 8) bludgeoning damage. If the target is Large or smaller, it must succeed on a DC 21 Strength saving throw or be pushed up to 15 feet away from the Unstable Mutation and knocked prone.
Mutated Claw. Melee Weapon Attack: +13 to hit, reach 15 ft., one target.
Hit: 17 (2d8 + 8) slashing damage. If the target is Large or smaller and the Unstable Mutation is grappling fewer than two creatures with this attack, the target is grappled (escape DC 21). While grappled in this way, the target is restrained.
Hurl Debris. Ranged Weapon Attack: +13 to hit, range 60/180 ft., one target.
Hit: 24 (3d10 + 8) bludgeoning damage. Each creature within 5 feet of the target must succeed on a DC 18 Dexterity saving throw or take 9 (2d8) bludgeoning damage from flying debris.
Catastrophic Rampage (Recharge 5–6). The Unstable Mutation moves up to its speed in a straight line without provoking opportunity attacks. During this movement, it can move through the spaces of Large or smaller creatures.
The first time it enters a creature’s space during this movement, that creature must make a DC 21 Dexterity saving throw. On a failed save, the creature takes 31 (4d10 + 9) bludgeoning damage and is knocked prone. On a successful save, it takes half as much damage and isn’t knocked prone.
The Unstable Mutation can move through nonmagical objects and structures as though they were difficult terrain, dealing 40 bludgeoning damage to each section it passes through.

Bonus Actions

Violent Seizure. One creature grappled by the Unstable Mutation takes 13 (2d12) bludgeoning damage. The Unstable Mutation then throws the creature to an unoccupied space on the ground it can see within 30 feet.
The thrown creature lands prone and takes 10 (3d6) bludgeoning damage. Each other creature within 5 feet of where it lands must succeed on a DC 18 Dexterity saving throw or take the same damage.

Reactions

Reactive Mutation. When the Unstable Mutation takes damage from a creature it can see within 30 feet, it moves up to half its speed toward that creature without provoking opportunity attacks.
If it ends this movement within reach of the triggering creature, it makes one Crushing Fist attack against it.

Legendary Actions

The Unstable Mutation can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature’s turn. The Unstable Mutation regains spent legendary actions at the start of its turn.
Advance. The Unstable Mutation moves up to half its speed.
Crushing Fist. The Unstable Mutation makes one Crushing Fist attack.
Groundbreaker (Costs 2 Actions). The Unstable Mutation slams the ground. Each creature within 15 feet of it must succeed on a DC 21 Strength saving throw or take 13 (2d12) bludgeoning damage and fall prone.
Rupture Growth (Costs 3 Actions). The Unstable Mutation violently sheds unstable tissue. Each creature within 20 feet of it must make a DC 19 Constitution saving throw, taking 22 (4d10) necrotic damage on a failed save or half as much damage on a successful one.
The Unstable Mutation then loses 10 hit points. This hit point loss can’t be reduced or prevented.