Burrow

Overview
Burrowing is a monster special quality, a movement mode.

Description
A creature with this movement mode can tunnel through dirt, sand, earth, and sometimes rock and masonry. Most burrowing creatures do not leave behind any sign of their passage, but some do leave tell-tale marks on the ground in the entry and exit points.

This is a potent defensive ability, since you can't target a burrowing creature.

It is an offensive ability as well, since it allows a creature to attack you by surprise, provided you don't spot it before it burrows.

Tactics
Sometimes, you can track subtle signs of underground movement that enable you to roughly estimate the general direction and speed of the creature.

Moreover, since a burrowing creature's combat routine usually involves a recurring pattern of attack and burrow, if you manage to hit it with an attack that deals damage over time while aboveground, it will keep damaging the creature even when underground.