Hermit Crab Swarm
Level 4Abilities
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.
This monster doesn't have a single mind (typically because it's a swarm of smaller creatures), and is immune to mental effects that target only a specific number of creatures. It is still subject to mental effects that affect all creatures in an area.
Each enemy in the swarm's space takes 2d8 piercing damage (DC 20 reflex save). Creatures that fail this save also take 1d4 bleed.
Description
When hermit crabs find a shell that is too large, they lie in wait for others to arrive and move into the shell, abandoning a possible replacement. This can form a large chain of queuing crabs waiting to upgrade their shells. Interruptions can aggravate the crabs, resulting in attacks against the unfortunate source of disruption.
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.