A creature with a burrowing speed can tunnel through sand, loose soil, or gravel, but treats areas of solid rock as impeded terrain. This movement works only through natural, undisturbed materials, and cannot be used to move through manufactured or constructed structures, such as walls, foundations, doors, portcullises, shutters, or any other 'made' thing. Using burrowing requires only as much concentration as walking, so the creature can attack or cast spells normally. Loose material collapses behind the creature 1 round after it leaves the area. Burrowing does not give the creature the ability to breathe underground, so when passing through loose material, the creature must hold its breath and take only short trips, or else it may suffocate.
A creature with burrowing must be able to trace line of effect to any creature it wishes to attack. Since line of effect is always bi-directional, a creature cannot use burrowing to make attacks while being immune to attacks itself.
Attacks of opportunity against creatures with burrowing rely on the attacking creature's ability to draw line of effect to the square the burrowing creature just left. That is, if the Burrowing creature is on the surface, and burrows into the ground, leaving a threatened square, the attacker probably has line of effect and can therefore make an attack of opportunity. However, passing under a creature while burrowing probably does not provoke attacks of opportunity, as the would-be attacker probably can't draw line of effect into the ground (unless he also has a burrowing speed, for example).
Creatures with a burrowing speed usually gain a +1 training bonus on Might checks, to show their strong, sturdy nature (even though checks to determine the success of burrowing are always made with the Movement skill).
- Prone: A creature with a burrowing speed cannot be made Prone, but any time they are subject to the Prone condition, they are instead Immobilized until they expend a move action to reorient themselves. Spending a move action to clear the Immobilized condition does not provoke attacks of opportunity.
- Difficult Terrain: Burrowing generally allows a creature to bypass difficult terrain, since they can just go under or around it, even when passing through the ground surface which is deemed difficult terrain (unless it is made of stone).