Nasurgeth

A creature with greater darkvision can see perfectly well in areas of darkness and dim light, though such vision is in black and white only. A creature with greater darkvision can see through even forms of magical darkness.

A monster with telepathy can communicate mentally with any creatures within the listed radius, as long as they share a language. This doesn't give any special access to their thoughts, and communicates no more information than normal speech would.

Lifesense allows a monster to sense the vital essence of living and undead creatures within the listed range. The sense can distinguish between the vitality energy animating living creatures and the void energy animating undead creatures, much as sight distinguishes colors.

60 feet. A nasurgeth's entropy grows even stronger underwater. All water within the aura is completely dark (as 4th-rank Darkness). Magical light with a counteract rank of 4th level or lower, along with magical light cantrips, are suppressed. A living creature entering or starting its turn in the aura takes 4d6 void damage, and the creature also takes an additional 2d10 cold damage if it's in water (DC 39 fortitude). If it fails, it's also Enfeebled 1 for 1 minute and pulled 10 feet toward the nasurgeth.

Trigger The nasurgeth takes slashing or piercing damage from a critical hit, or a swallowed creature cuts itself free Effect Darkness and void energy spill out from the nasurgeth's wound, dealing 8d8 void damage to creatures within 20 feet (DC 40 fortitude).

A nasurgeth caught in sunlight is Stunned 2 and Clumsy 2.

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.

Requirements A creature is Grabbed or Restrained in the nasurgeth's jaws

The nasurgeth breaks a tooth off in the target, who takes 3d10 bleed and is no longer grabbed or restrained. If the target is adjacent to a surface, the tooth also pins it in place, making it Immobilized (Escape).

The nasurgeth barrels forward with their mouth open, Swimming twice in a straight line and moving through the spaces of Huge or smaller creatures. The nasurgeth deals the damage of their jaws Strike to each creature whose space they enter (DC 45 reflex). Any creature that critically fails is automatically Swallowed Whole.

Huge, (2d10+9) bludgeoning, Rupture 40 A living creature that ends its turn swallowed whole by a nasurgeth becomes Drained 1 or increases its drained condition by 1, and the nasurgeth gains 20 temporary Hit Points. A creature whose drained condition increases to 5 in this way dies. 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.

Trigger The monster's last action was a successful Strike that lists Improved 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 as a free action. This attempt neither applies nor counts toward the creature's multiple attack penalty. The monster can instead use Improved Grab as an action and choose one creature it's grabbing or restraining with an appendage that has Improved Grab to automatically extend that condition to the end of the monster's next turn.