Cobbleswarm
CREATURE 2Busy road builders might unknowingly use cobble mites in construction.
Cobble mites resemble squarish stones a few inches across with mouths like split geodes. Though indolent and harmless alone, they're dangerous in large groups.
A cobbleswarm's tremorsense is a precise sense out to 40 feet and an imprecise sense out to 80 feet. A cobbleswarm can't sense anything beyond the range of its tremorsense.
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.
The cobbleswarm's space is difficult terrain.
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.
The cobbleswarm attempts an Athletics check and compares the result to the Fortitude DC of each creature in its space. This counts as two attacks for the cobbleswarm's multiple attack penalty.
Critical Success The creature falls Prone, takes 1d6 bludgeoning damage, and is Grabbed by the cobbleswarm until the end of the cobbleswarm's next turn.
Success The creature falls prone.
Each foe in the cobbleswarm's space takes 2d4 bludgeoning damage (DC 17 basic Reflex save).