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 32; Fort +24, Ref +21, Will +19
HP 230; Immunities bleed, death effects, disease, paralyzed, poison, unconscious; Resistances cold 10
Speed 20 feet, swim 35 feet
Melee Claw +26 (agile, unarmed), Damage 3d6+13 slashing plus Grab
Melee Jaws +26 (unarmed), Damage 3d10+13 piercing
Aquatic Camouflage
When fully submerged in water, the drenchdead can Hide from other creatures even if it doesn't have cover against them and isn't Concealed from them.
Drag Down
Requirements The drenchdead is swimming in water at least 10 feet deep
Effect The drenchdead attempts an Athletics check to Grapple an adjacent creature (on nearby land or in the water). On a success against a creature on land, in addition to the normal effects of Grapple, the drenchdead pulls the creature into the water into a space adjacent to itself. If the creature is already in the water, on a success, in addition the normal effects of Grapple, the drenchdead drags the creature 10 feet deeper, moving 10 feet with the creature. Moving a creature into water or deeper into water using Drag Down is forced movement for the target creature, but not for the drenchdead.
Drowning Touch(incapacitation, occult, water)
The drenchdead touches a creature and causes water from its own body to flow into the creature's lungs. If the creature can't breathe water, it must attempt a DC 32 Fortitude save.
Success The creature is unaffected and is temporarily immune to Drowning Touch for 24 hours.
Critical Failure The creature chokes on the water and runs out of air. It falls Unconscious and starts drowning. If the creature is above water, it recovers from drowning as soon as it succeeds at a saving throw against suffocation.
Surface Skimmer
A drenchdead submerged in water has cover from attacks made by creatures out of the water.
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.