Niddioggr, the Devouring Serpent (CR 12)
"I gnaw at the roots of Yggdrasil, and when the World Tree falls, so too shall the
realms."
Gargantuan Dragon (Serpent), Chaotic Evil
Armor Class: 19 (Natural Armor)
Hit Points: 230 (20d12 + 100)
Speed: 50 ft., Climb 30 ft., Swim 50 ft.
Description:
Niddioggr, the Devouring Serpent, is an ancient, monstrous entity with the body of a
massive serpent and the features of a dragon. Its scales are dark as the void,
glistening with venom and rot. Its immense, coiling form wraps around the roots of
Yggdrasil, gnawing endlessly at the World Tree. With every bite, it weakens the
foundation of the realms, bringing decay and death in its wake.
The serpent’s head is adorned with rows of jagged, shark-like teeth, and its eyes
glow with an eerie, poisonous green light. Its breath is a cloud of toxic, acrid fumes
that choke the life from anything nearby. It is said that the end of the world will
come when Niddioggr consumes the last of Yggdrasil’s roots, causing the
destruction of all the Nine Realms. The serpent is not just a mindless predator—it is
a force of entropy and destruction that seeks to bring the realms into ruin.
Though it is typically immobile, coiled around the World Tree, it can be summoned
by dark sorcerers or gods who seek to unmake the worlds. Niddioggr speaks in a
low, hissing voice, full of venom and ancient malice, offering false promises of
power to those willing to bargain with it.
Stat Block (CR 12)
Stat Value
24
Strength
(+7)
16
Dexterity
(+3)
Constituti 21
on (+5)
Intelligen 18
ce (+4)
Stat Value
16
Wisdom
(+3)
19
Charisma
(+4)
Saving Throws: Dex +8, Con +10, Wis +8, Cha +9
Skills: Perception +13, Stealth +8
Damage Immunities: Poison, Psychic
Damage Resistances: Fire, Lightning
Condition Immunities: Blinded, Charmed, Frightened, Paralyzed
Senses: Blindsight 60 ft., Darkvision 120 ft., Passive Perception 23
Languages: Draconic, Infernal, Telepathy 120 ft.
Challenge Rating: 12 (8,400 XP)
Traits
Legendary Resistance (3/Day).
If Niddioggr fails a saving throw, it can choose to succeed instead.
Serpent’s Regeneration.
At the start of each of Niddioggr’s turns, it regains 10 hit points. If it takes fire or
radiant damage, this trait doesn’t function on that turn.
Aura of Decay. (Passive)
Any creature that starts its turn within 30 feet of Niddioggr takes 10 (3d6) poison
damage as the serpent’s corrupting aura saps their strength and vitality.
Poisonous Breath. (Recharge 5-6)
Niddioggr exhales a cloud of toxic fumes in a 60-foot cone. Each creature in that
area must make a DC 18 Constitution saving throw or take 56 (16d6) poison
damage on a failed save, or half as much on a successful one. Creatures that fail
the saving throw are also poisoned for 1 minute.
Actions
Multiattack.
Niddioggr makes three attacks: one with its bite, one with its tail, and one with its
constrict.
Bite.
Melee Weapon Attack: +12 to hit, reach 15 ft., one target.
Hit: 27 (4d8 + 7) piercing damage plus 14 (4d6) poison damage.
Tail.
Melee Weapon Attack: +12 to hit, reach 20 ft., one target.
Hit: 22 (3d10 + 7) bludgeoning damage.
Constrict.
Melee Weapon Attack: +12 to hit, reach 15 ft., one target.
Hit: 24 (4d6 + 7) bludgeoning damage and the target is grappled (escape DC 18).
Until the grapple ends, the target is restrained, and Niddioggr cannot constrict
another target.
Legendary Actions
Niddioggr 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. Niddioggr regains spent legendary actions at the start of its turn.
Tail Lash. Niddioggr makes one tail attack.
Poisonous Spit (Costs 2 Actions). Niddioggr spits a venomous glob at a
creature it can see within 60 feet. The target must make a DC 18 Dexterity
saving throw or take 14 (4d6) poison damage and be blinded until the
end of their next turn.
Slithering Retreat (Costs 2 Actions). Niddioggr can move up to half its
speed without provoking opportunity attacks.
Lair Actions (If the party fights Niddioggr within its lair, or the roots of
Yggdrasil)
On initiative count 20 (losing initiative ties), Niddioggr can take a lair action to
cause one of the following effects:
Toxic Growth. The roots of Yggdrasil twist and surge, creating a patch of
corrupt vegetation. A 15-foot radius of difficult terrain becomes filled
with toxic plants. Each creature that starts its turn in this area takes 10 (3d6)
poison damage.
Shattered Roots. Niddioggr causes the ground beneath the party to
tremble, causing a 10-foot-wide crack to form in the earth. Each creature in
that area must make a DC 18 Dexterity saving throw or fall prone. The
area becomes difficult terrain until the end of the next round.
Yggdrasil’s Fading Light. Niddioggr’s influence over the roots of Yggdrasil
darkens the area. The area within 30 feet of Niddioggr becomes magically
darkened, creating dim light even in daylight or magical light, lasting until
the end of Niddioggr’s next turn.
Tactics
Takes advantage of its high mobility—using its Serpent’s
Regeneration to stay healthy, and moving between turns to stay out of
range of most melee attackers.
Uses Poisonous Breath to weaken large groups of enemies, keeping them
poisoned.
Targets spellcasters and weak enemies first, using Constrict to restrain
them.
Uses its Legendary Actions to harass and disable enemies, preventing
them from taking full actions against it.
Loot
If Niddioggr is defeated, it may drop:
Venom-Dripped Fang. A magical weapon or component capable of inflicting
poison damage.
Heart of the Devouring Serpent. A dark magical artifact capable of
summoning venomous creatures or controlling poison-based magic.
Yggdrasil’s Withered Root. A rare magical material that can be used for
crafting powerful poison-based weapons or armor.
Final Thoughts
Niddioggr is a menacing and ancient creature that embodies decay and destruction.
Its high mobility, strong poison-based abilities, and regeneration make it an
excellent CR 12 challenge for parties of high level. The serpent can wear down a
party with poison and strategic movement, making it a formidable adversary that
can take advantage of the environment in unexpected ways.
Venom-Dripped Fang
Weapon (Dagger), Very Rare (Requires Attunement)
Description:
This sleek dagger is forged from the fang of Niddioggr, the Devouring Serpent. The
blade glows with an eerie, greenish hue, as if it’s permanently soaked in venom.
When wielded, the blade seems to pulse with the rhythm of a heartbeat, and the
scent of death and decay follows its every movement. The blade’s edge is razor-
sharp, capable of slicing through armor as though it were paper.
The fang’s venom is potent, lingering in the bloodstream of its victims, slowly
draining their vitality and weakening their resolve. It is said that only those with an
innate connection to poison or venom can truly wield the weapon without
succumbing to its corrupting effects.
Weapon Properties:
Weapon Type: Dagger
Rarity: Very Rare
Damage: 1d6 piercing damage + 2d6 poison damage
Weight: 1 lb
Properties: Finesse, Light
Requires Attunement by a creature with poison immunity or
resistance
Abilities & Features:
Venomous Strike.
When you hit a creature with this dagger, the target must make a DC 16
Constitution saving throw or take 2d6 poison damage and be poisoned for 1
minute. A creature poisoned this way can make the saving throw again at the end of
each of its turns, ending the effect on itself on a success.
Serpent's Curse. (Recharge 5-6)
As an action, you can imbue the blade with the essence of Niddioggr’s venom,
causing it to pulse with toxic energy. The next attack you make with the dagger
deals an additional 3d6 poison damage, and the target must make a DC 18
Constitution saving throw or be paralyzed for 1 minute. The paralysis can be
ended by another creature using an action to shake the target or by the target
succeeding on a saving throw at the end of each of its turns.
Contagious Venom.
If you score a critical hit with this dagger, the target is injected with a highly
virulent form of poison. All creatures within 10 feet of the target must make a DC
16 Constitution saving throw or take 2d6 poison damage and be poisoned for
1 minute.
Poisoned Blades. (Passive)
You can coat the dagger in poison as a bonus action. The blade remains coated in
poison for 1 hour, and any creature struck by the dagger takes 1d6 poison
damage (in addition to the dagger's normal damage) until the poison is washed off.
You can coat the dagger in poison this way once per short rest.
Curse (Optional DM Feature):
While attuned to the Venom-Dripped Fang, you feel an overwhelming urge to use it
in combat. If you do not deal damage with the weapon at least once every 24 hours,
you must make a DC 16 Wisdom saving throw or suffer disadvantage on all
Wisdom saving throws and ability checks for the next 24 hours.
Final Thoughts:
The Venom-Dripped Fang is an ideal weapon for assassins, poisoners, or any
character with a focus on stealth and control. Its ability to poison and paralyze
targets makes it excellent for disrupting spellcasters or taking out enemies in a
more subtle manner. Its deadly venom and unique properties make it a valuable
treasure for any party.
Heart of the Devouring Serpent
Wondrous Item, Legendary (Requires Attunement by a Sorcerer, Warlock, or Wizard)
Description:
The Heart of the Devouring Serpent is a pulsating, jet-black gemstone that
hums with dark energy. This ancient artifact is said to be the heart of Niddioggr, the
Devouring Serpent, ripped from its chest as a means to control its power. The gem
radiates an aura of toxic magic, corrupting everything around it. It can be held in
the palm or worn as a pendant, though it demands a price for its power.
The artifact grants its wielder dominion over poison and venom-based magic, giving
them the ability to summon venomous creatures and even bend the poison of the
world to their will. However, the Heart feeds on the essence of life and the user's
sanity, and those who are not careful risk becoming twisted by its corrupting
influence.
Abilities & Features:
Poison Mastery.
While attuned to the Heart of the Devouring Serpent, you gain the following
benefits:
You have resistance to poison damage.
You can cast the following spells without expending a spell slot. Once you
cast each of these spells in this way, you can’t do so again until you finish a
long rest:
o Poison Spray (Cantrip)
o Stinking Cloud (1st level)
o Cloudkill (5th level)
Additionally, when you deal poison damage, you can add your Charisma modifier
(minimum of +1) to the damage dealt.
Summon Venomous Beast. (1/Day, Action)
You can use the Heart of the Devouring Serpent to summon a venomous creature.
You can choose from the following:
Giant Poisonous Snake (CR 1/4)
Giant Scorpion (CR 3)
Venom Troll (CR 7)
Venomous Hydra (CR 10)
The creature obeys your commands for 1 hour before disappearing. Once this
feature is used, it cannot be used again until the next dawn.
Serpent’s Corruption. (Passive)
The Heart constantly drains the sanity of its wielder. After attuning to it, you must
make a DC 15 Wisdom saving throw at the end of every long rest. On a failure,
you gain a level of madness (as per the Madness rules in the Dungeon Master's
Guide) for 24 hours. This madness cannot be removed by any magical means
except Greater Restoration or Wish.
Devouring Influence. (Once Per Long Rest, Action)
Once per long rest, the Heart allows you to cast Contagion without expending a
spell slot. You can choose the Filth Fever, Flesh Rot, or Sepsis effects.
Additionally, when you deal damage to a creature with a poison-based attack or
spell, you may force them to make a DC 18 Constitution saving throw or
become paralyzed for 1 minute, as their body is ravaged by the venom coursing
through it.
Curse (Optional DM Feature):
The Heart of the Devouring Serpent is a dark artifact, and its power comes with a
heavy price. Over time, the artifact corrupts the mind and body of its wielder,
causing them to become more consumed by poison, venom, and madness.
If the wielder ever drops to 0 hit points while attuned to the Heart, their
body is consumed by the serpent’s venom, and they are resurrected as a
venomous undead (DM’s discretion) under the Heart’s control.
The wielder must also make a DC 18 Wisdom saving throw each time they
kill a creature using poison or venom-based magic. On a failure, they suffer a
permanent +1 to their Madness level (up to a maximum of 3).
Final Thoughts:
The Heart of the Devouring Serpent is an incredibly potent magical artifact,
capable of granting its wielder unrivaled mastery over poison and venom. Its ability
to summon venomous creatures and its mastery of toxic spells make it a perfect
choice for casters who specialize in poison. However, its curse and draining
influence on the wielder’s sanity ensure that its use comes at a steep cost, and only
those with immense willpower should seek to wield it.
