Giant Hermit Crab
CREATURE 5Lucky hermit crabs with plentiful resources can live for decades and grow to tremendous sizes, often with magical help. Too large for most natural shells, giant hermit crabs use a variety of debris instead, including wagons, boats, treasure chests, and even abandoned pieces of giant armor.
Hermit crabs have hard exoskeletons like other crabs, but with much weaker abdomens. They find and "wear" shells as homes and protection, getting around with their front legs and claws. Surprisingly fierce, hermit crabs fight for new shells as they grow bigger, using an assortment of hollow alternatives as substitutes when shells of the right size can't be found.
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.
1d8+6 bludgeoning, DC 22 basic Fortitude
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.
The hermit crab curls fully into its shell to protect itself. This gives it a +4 circumstance bonus to AC, removes its weakness to bludgeoning damage, and grants it resistance 5 to piercing and slashing damage.
The only actions the hermit crab can use while in this state are Protective Pinch and Interact to come out of its shell.
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.