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Gloomforged Colossus

Some sages call them obsidian wardens—machines of living dark alloy rumored to be the product of a war between a shadow cult and a cabal of dwarven forgemasters. Myths say a fallen star or void-spear is the seed that awakens each one. Towns near their graves claim bad harvests and pale children who speak to the dark stones.

Monsters
Huge monstrosity · CR 14 · Unique

Gloomforged Colossus

A siege-scale animated construct fused with living shadow. Built or birthed to hold and corrupt important ground, it is equal parts battlefield engine and psychological weapon.
AC19
HP210/210
CR14
Init
STR
DEX
CON
INT
WIS
CHA
ConditionsNone

Combat

AC 19 · HP 210 · CR 14

Gloomforged Colossus

Huge monstrosity (construct (shadow-infused)), neutral evil
Armor Class19
Hit Points210 (20d12 + 100)
Speed
Walk 40 ft.,
Climb 20 ft.
STR
DEX
CON
INT
WIS
CHA
Saving ThrowsStrengthConstitutionWisdomCharisma
SkillsAthleticsPerceptionStealthArcana
Damage Resistances
cold,
necrotic,
bludgeoning, piercing, and slashing from nonmagical attacks
Immunities
poisoned,
charmed
Weaknesses
Vulnerable to radiant damage (takes extra damage from radiant sources),
Bright light (sunlight or daylight spells) suppresses its Shadow Renewal and reduces Umbral Aura radius by half while in effect
Senses
Darkvision 120 ft.,
Passive Perception 17
Languages
Common,
Telepathy 120 ft.
Challenge14
Proficiency Bonus+5
Passive Perception17
Magic Resistance. The colossus has advantage on saving throws against spells and other magical effects.
Shadow Aegis. If the colossus takes 60 or more damage from a single attack, it can use a reaction to emit a burst of shadow that grants it resistance to all damage until the end of its next turn. Usable once per short rest.
Magic Weaponry. The colossus counts as magical for the purpose of overcoming resistance and immunity to nonmagical attacks.
Feeding Strike. When the colossus reduces a creature to 0 hit points with its Slam, that creature's dying essence feeds the colossus. The colossus regains 10 hit points and the area within 10 feet of the corpse becomes shadowstained for 1 hour.
Umbral Aura. A continuous aura of dim shadow extends 10 feet from the colossus. Nonmagical light sources that illuminate the area have their radius halved while within the aura.
Anchored Form. The colossus can attempt to resist one effect that would teleport it or force it to move against its will. It has advantage on the saving throw.
Shadow Step. Three times per day the colossus can step through shadow and teleport up to 60 feet to an unoccupied space in dim light or darkness it can see.
Shadow Renewal. If the colossus starts its turn in dim light or darkness it regains 10 hit points.
Legendary Resistance. If the colossus fails a saving throw, it can choose to succeed instead. It can use this ability three times and regains all uses after a long rest.

Spells

Darkness (innate) (cantrip, evocation). At will: Darkness (as the spell).
Fear (innate) (level 3, illusion). 3/day: Fear (as the spell, cast at 3rd level).
Blight (innate) (level 4, necromancy). 1/day: Blight (as the spell).

Actions

Multiattack. The colossus makes two Slam attacks. If both hit the same target, the target must succeed on a Strength saving throw or be knocked prone.
Slam. Melee Weapon Attack: to hit, reach 10 ft., one target. Hit: 24 () bludgeoning damage plus 10 () necrotic damage.
Umbral Shockwave. The colossus stomps the ground. Each creature in a 30-foot cone must make a Dexterity saving throw, taking 45 () force damage on a failed save, or half as much on a success. Creatures that fail the save are also pushed 15 feet and knocked prone. Objects in the area that are not worn or carried are automatically destroyed if their AC is 15 or lower.
Aura of Dread. The colossus targets one creature it can see within 120 feet. The target must succeed on a Wisdom saving throw or become Frightened for 1 minute. A frightened target can repeat the saving throw at the end of each of its turns, ending the effect on a success. If the target is already frightened, it takes 18 () psychic damage instead on a failed save.
Shadow Spire (Recharge 5-6). The colossus makes one ranged attack against a point it can see within 150 feet. All creatures within a 10-foot radius of that point must make a Constitution saving throw, taking 36 () necrotic damage on a failed save, or half as much damage on a success. Undead creatures have disadvantage on the saving throw.

Reactions

Parry. Parry. The colossus adds +3 to its AC against one melee attack that would hit it. To do so, the colossus must see the attacker and be wielding no weapon.

Legendary Actions

Slam. Slam. The colossus makes one Slam attack.
Relentless Advance. Move. The colossus moves up to half its speed without provoking opportunity attacks.
Shadow Pulse (costs 2 actions). Shadow Pulse. The colossus emits a pulse of crushing shadow in a 20-foot radius. Creatures in the area must succeed on a Constitution saving throw or take 18 () necrotic damage and have disadvantage on their next attack roll.
Role
Frontline controller and boss
Built for
14

Gear

  • Heartstone (colossus core) (Treasure, Very valuable)A fist-sized obsidian-black gem pulsing with faint purple light. It can be used as a rare crafting component for shadow-infused items or sold to collectors.

Notes for the game master

Proficiency bonus +5
Spell save DC 18 for innate spells (8 + proficiency + Charisma modifier)

Tactics

  1. Opening

    Begin fight from range by anchoring an area with Shadow Spire if needed to break ranks, then close quickly using its high movement and powerful Slam to establish control. Use Aura of Dread to immediately pressure the enemy morale and force concentration checks.

  2. Mid-fight

    Keep frontline control with Umbral Shockwave to push and knock down melee fighters, use Aura of Dread to sow fear and isolate spellcasters, and follow up with Slam attacks on prone or incapacitated targets.

  3. End of the fight

    Use Shadow Spire to cripple or heavily damage remaining foes, then focus slam attacks on the weakest bright-threat or spellcaster while refusing to be flanked. If reduced below half HP, become more defensive and use legendary actions to reposition.

  4. Retreat

    If reduced to 25% HP the colossus attempts to retreat into a pocket of deep shadow by teleporting 60 feet into dim light using its innate shadow step ability (if available) or withdraws to a prepared lair if within 300 feet. It will fight to the death if protecting a hoard or lair nexus.

How it fights

Open with Shadow Spire at range to fracture enemy lines or punish grouped spellcasters.
Use Umbral Shockwave when foes bunch up to maximize knockdowns and push them into difficult terrain or hazards.
Make use of Legendary Actions each round to reposition and keep priority targets within reach.

Who it attacks first

Spellcasters and support characters that can heal or dispel magic
Ranged attackers who stay behind cover
Frontline characters who threaten its control of the battlefield

Works well with

Works well with minions that can force enemies into tight formations for its cone attacks.
Cultists who can conjure darkness or debuffs amplify its control abilities.
Ranged fighters that bait foes into the colossus' reach benefit from its pushing and prone effects.

How to beat it

Radiant damage dealers and bright light spells disrupt its shadow abilities.
High mobility and ranged attacks that can avoid its cone abilities reduce its effectiveness.
Spells and abilities that grant immunity to frightened condition negate its Aura of Dread.
Dispel magic and targeted counterspells can deny its Shadow Spire when it attempts longer casting or recharge interactions.

Ways to avoid a fight

Appeasement by offering other shadow artifacts or the heartstones of lesser constructs.
Trickery by mimicking the voices of trapped victims over telepathy to lure it away from a target.
Using high-power radiant sources or a temple ritual to temporarily stun or repel it for bargaining.

Ecology

A towering humanoid construct of black-fused iron and living shadow. Broad shoulders, long segmented arms ending in massive hands, and a crown-like crest of jagged metal shards. Its surface is matte black but veins of purple shadow pulse beneath the metal like slow-moving smoke. Eyes are two vertical slits of cold, pale violet light.

Behavior

Cold, methodical, and territorial. The colossus moves with purposeful slowness but reacts instantly to threats. It prioritizes breaking the cohesion of a party and targeting leaders and spellcasters. It is not prone to mercy and uses fear as a tool; it can be bartered with by offering shadow-forged artifacts or the heartstone of a defeated colossus.

How it lives

Colossi are rare constructs created at sites where planar shadows press against the Material Plane. They feed on ambient fear and the decay of life, slowly turning the immediate environment toward blight. Some are made by cabals of shadow mages or as guardians for cults. When a colossus dies, its remains erode into a maw of black iron that can taint the soil for years.

Lair

The lair is a fractured plateau where shadows cling to stone. Lair actions occur on initiative count 20 (losing initiative ties): 1) A wall of shadow rises, creating difficult terrain in a 30-foot line; 2) an echo of the colossus' voice causes all creatures in the lair to make a DC 16 Wisdom saving throw or be dazed (disadvantage on attack rolls) until the end of their next turn; 3) patches of ground become shadowstained, imposing disadvantage on Perception checks to notice hidden creatures until cleansed. The lair often contains ritual braziers that strengthen the colossus' recharge on Shadow Spire by 1 (DM choice).

Habitat
Ruined keeps, shadow-touched valleys, warped forests, mountain passes

Signs that it is near

Trailing shadow-smoke rising from footprints
Wilted plants and frost-like black motes
Deep, metallic scraping sounds like a distant hammer

Tags

construct,
shadow,
boss,
controller,
lair

Lore

Some sages call them obsidian wardens—machines of living dark alloy rumored to be the product of a war between a shadow cult and a cabal of dwarven forgemasters. Myths say a fallen star or void-spear is the seed that awakens each one. Towns near their graves claim bad harvests and pale children who speak to the dark stones.

What drives it

To hold and spread its shadow domain. It defends loci of planar weakness and consumes sources of light and joy to fuel its existence.

After the fight

The colossus leaves a long-lasting shadow-stain on the earth and stone where it falls. Plants die within a 300-foot radius and the area remains under dim light from the lingering umbral residue for 24 hours. Any creature that sleeps within the stain must succeed on a DC 15 Wisdom saving throw or suffer nightmares and lose one level of exhaustion. The colossus' heartstone can be harvested by skilled artificers; it is a faintly pulsing black gem worth considerable value and useful as a rare crafting component for shadow-infused items.

“Myths say a fallen star or void-spear is the seed that awakens each one.”
From its lore

Variants

Twinned Colossus: Two smaller colossi (Huge) bound together with shared hit points but separate actions.
Ancient Gloomforged: CR 17 variant with higher HP, an extra Legendary Action, and a more potent Shadow Spire.
Warded Colossus: Built to guard a specific relic; has additional protective runes that grant spell reflection 1/day.

Hooks

Plot hooks

A colossus has been seen marching through a trade route, crushing caravans and leaving blighted ground.
A cult seeks to awaken a dormant colossus beneath a ruined fortress and needs the party to gather the final ritual components.
A village offers a reward for the heartstone taken from a colossus that has been terrorizing their valley.

How to use it

As a planned lair guardian defending a cult's ritual site.
As an ambush placed to block a mountain pass or ruined bridge.
As an arena or set-piece boss where terrain gives both cover and elevation for players to exploit.

Treasure

Heartstone gem (very valuable and useful in shadow item crafting)
Discarded shadow-forged metal shards (can be used as raw materials for magical smithing)
Occasional ritual parchments or small cultist offerings

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