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From Pathfinder Lost Omens Monsters of Myth, which isn't enabled.

Ulgrem-Axaan

CREATURE 7
UNIQUELARGEAMPHIBIOUSBEASTCHAOTICEVILUNDEADUNHOLY
Perception +18; darkvision, wavesense (imprecise) 60 feet
Languages Necril, Wildsong; (can't speak any language)
Skills Athletics +17, Deception +15, Intimidation +17, Stealth +16 (+20 in water)
Str +6, Dex +4, Con +4, Int -2, Wis -1, Cha +4
Frozen Contemplation

Being frozen stops the constant pain Ulgrem-Axaan has experienced since its death. Ulgrem-Axaan has fast healing 5 while in severe cold or colder environments, or for 1 round after taking cold damage.

Wavesense (Imprecise) 60 feet

This sense allows a monster to feel vibrations caused by movement through a liquid. It's an imprecise sense with a limited range (listed in the ability). Wavesense functions only if monster and the subject are in the same body of liquid, and only if the subject is moving through the liquid.

AC 24; Fort +18, Ref +15, Will +12; +2 status to all non-primal emotion effects
HP 130, void healing; Immunities bleed, death effects, disease, paralyzed, poison, unconscious; Weaknesses fire 5; Resistances cold 10, electricity 5, piercing 5
+2 Status to All Saves vs. Non-primal Emotion Effects
Baleful Glare (aura, emotion, fear, visual)

15 feet. Creatures entering or starting their turn in the emanation that can see Ulgrem-Axaan must succeed at a DC 22 Will save or be Frightened 1 (Frightened 2 on a critical failure). A creature that succeeds at its save is temporarily immune to baleful glare for 1 minute.

Ferocity

Trigger The monster is reduced to 0 HP.
Effect The monster avoids being knocked out and remains at 1 HP, but its Wounded value increases by 1. When it is Wounded 3, it can no longer use this ability

Territorial Rage
Trigger A creature comes within melee reach of Ulgrem-Axaan while it's burrowed underground or underwater
Effect Ulgrem-Axaan lunges and makes a jaws Strike against the creature, which is Off-Guard against the attack and takes an additional 1d6 damage on a hit.
Void Healing

A creature with void healing draws health from void energy rather than vitality energy. It is damaged by vitality damage and is not healed by vitality healing effects. It does not take void damage, and it is healed by void effects that heal undead.

Speed 25 feet, burrow 10 feet, swim 30 feet
Melee Jaws +18 (reach 10, unarmed), Damage 2d12+8 piercing plus Grab
Melee Tail +18 (agile, reach 10), Damage 2d8+8 bludgeoning plus Grab
Aquatic Ambush

30 feet

Requirements The monster is hiding in water and a creature that hasn't detected it is within the listed number of feet.
Effect The monster moves up to its swim Speed + 10 feet toward the triggering creature, traveling on water and on land. Once the creature is in reach, the monster makes a Strike against it. The creature is Off-Guard against this Strike.

Swallow Whole (attack)

Medium, 1d12+8 bludgeoning, Rupture 18

The monster attempts to swallow a creature of the listed size or smaller that it has grabbed or restrained in its jaws or mouth. If a swallowed creature is of the maximum size listed, the monster can't use Swallow Whole again. If the creature is smaller than the maximum, the monster can usually swallow more creatures; the GM determines the maximum. The monster attempts an Athletics check opposed by the grabbed creature's Reflex DC. If it succeeds, it swallows the creature. The monster's mouth or jaws no longer grab a creature it has swallowed, so the monster is free to use them to Strike or Grab once again. The monster can't attack creatures it has swallowed.

A swallowed creature is Grabbed, is Slowed 1, and has to hold its breath or start suffocating. The swallowed creature takes the listed amount of damage when first swallowed and at the end of each of its turns while it's swallowed. If the victim Escapes this ability's grabbed condition, it exits through the monster's mouth. This frees any other creature grabbed in the monster's mouth or jaws. A swallowed creature can attack the monster that has swallowed it, but only with unarmed attacks or with weapons of light Bulk or less. The swallowing creature is Off-Guard against the attack. If the monster takes piercing or slashing damage equaling or exceeding the listed Rupture value from a single attack or spell, the swallowed creature cuts itself free. A creature that gets free by either Escaping or cutting itself free can immediately breathe and exits the swallowing monster's space.

Effect: Engulf and Swallow Whole

If the monster dies, a swallowed creature can be freed by creatures adjacent to the corpse if they spend a combined total of 3 actions cutting the monster open with a weapon or unarmed attack that deals piercing or slashing damage.

Unnatural Vengeance

Ulgrem-Axaan gains a +1 circumstance bonus to attack and damage rolls against undead.

Voltaic Blow (electricity)
Requirements Ulgrem-Axaan has a creature Grabbed with its tail
Effect An electric shock passes through Ulgrem-Axaan's tail, dealing 2d4+8 electricity damage to the creature (DC 25 basic Fortitude save).
Grab

Requirements The monster's last action was a successful Strike that lists Grab in its damage entry, or the monster has a creature Grabbed or Restrained
Effect If used after a Strike, the monster attempts to Grapple the creature using the body part it attacked with. This attempt neither applies nor counts toward the creature's multiple attack penalty.

The monster can instead use Grab and choose one creature it's grabbing or restraining with an appendage that has Grab to automatically extend that condition to the end of the monster's next turn.

Pathfinder Lost Omens Monsters of MythOGL