Tremorsense allows a monster to feel the vibrations through a solid surface caused by movement. It is an imprecise sense with a limited range (listed in the ability). Tremorsense functions only if the monster is on the same surface as the subject, and only if the subject is moving along (or burrowing through) the surface.
AC 31; Fort +21, Ref +18, Will +15
HP 140; Immunities poison
Attack of Opportunity
Trigger A creature within the monster's reach uses a manipulate action or a move action, makes a ranged attack, or leaves a square during a move action it's using.
Effect The monster attempts a melee Strike against the triggering creature. If the attack is a critical hit and the trigger was a manipulate action, the monster disrupts that action. This Strike doesn't count toward the monster's multiple attack penalty, and its multiple attack penalty doesn't apply to this Strike.
The monster deals the listed amount of damage to any number of creatures Grabbed or Restrained by it. Each of those creatures can attempt a basic Fortitude save with the listed DC.
Requirements A drained creature is grabbed by the chuul's tentacles
Effect The creature takes 3d6 mental damage.
Swamp Stride
The Voidbracken chuul ignores difficult terrain and greater difficult terrain in swamps.
Tentacle Transfer
Requirements The Voidbracken chuul has a creature Grabbed
Effect The chuul transfers the grabbed creature from its claws to its tentacles, or vice versa. The creature is exposed to the chuul's draining venom when transferred into the tentacles and at the start of each of the chuul's turns if it remains grabbed by the tentacles.
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.