What actions can a burrowed creature take?

Question

A player in my upcoming game wants to play a burrowing race. I couldn't find rules about what sort of actions a burrow creature can take.

Do rules exist for burrowing creatures:

• Attacking from underground?
• Getting cover underground?
• Casting spells underground?

Note: I see this question has been answered for 4E, but this question is specifically about RAW Pathfinder.

Answer 1

Rules as Written, Burrow is undefined in Pathfinder.

The helpful folks at pathfindersrd have the rules for Burrow appended with the following note:

Burrow details were not included in the Pathfinder Roleplaying Game so the details shown here were copied from d20srd.org.

RAW cannot help you here.

That said, we take the 3.5 rules, as they did:

A creature with a burrow speed can tunnel through dirt, but not through rock unless the descriptive text says otherwise. Creatures cannot charge or run while burrowing. Most burrowing creatures do not leave behind tunnels other creatures can use (either because the material they tunnel through fills in behind them or because they do not actually dislocate any material when burrowing); see the individual creature descriptions for details.

This tells us a few things on its own:

• Burrowing is a form of movement, not a status condition.
• A creature cannot use the Charge or Run actions using burrow movement.

Since burrowing is a form of movement, the condition applied isn't "being burrowed," but rather, "being inside a solid object." Incorporeal creatures have rules for this in Pathfinder:

Enemies have total concealment (50% miss chance) from an incorporeal creature that is inside an object. In order to see beyond the object it is in and attack normally, the incorporeal creature must emerge. An incorporeal creature inside an object has total cover, but when it attacks a creature outside the object it only has cover, so a creature outside with a readied action could strike at it as it attacks.

I would give Burrowing creatures the same options. While "burrowed," they

• Can move
• Can use spells, abilities, and items with themselves as the target
• Have total concealment (and total cover) from everything.
• Cannot see outside their burrow - but might be able to make perception checks to hear.
• Can emerge as a free action

While "emerged," a they

• Trigger readied actions from any enemy that readied to attack when they emerged.
• Can attack, cast spells, etc. as normal
• Can see outside their burrow, and be seen as normal.
• Have cover (but not total cover) from everything, and everything has cover from them.
• Can submerge as a free action, even in the same turn as they emerged.

Addendum: Grappling

There's nothing I can see that would stop them from grappling someone, pulling them into a burrow, and leaving them there. You may wish to create a house-rule that would allow a creature who gets buried thusly to dig themselves out before they suffocate.

Answer 2

Making a few additions to Tim C's excellent answer:

Incorporeal creatures have an innate sense of direction and can move at full speed even when they cannot see.

This line, which burrowing creatures lack, implies that creatures in objects are Blinded while fully submerged (i.e., not attacking). Since burrowing creatures lack this line, in addition to the usual penalties to AC and Dexterity for being Blinded, they "must make a DC 10 Acrobatics skill check to move faster than half speed". It would be reasonable to waive this requirement for creatures with Tremorsense (I certainly would!), but doing so is not RAW.

Tim C's interpretation that other creatures will also have Cover from a burrowed creature is not mentioned in the Incorporeal rules, but stems from the Cover rules:

To determine whether your target has cover from your ranged attack, choose a corner of your square. If any line from this corner to any corner of the target’s square passes through a square or border that blocks line of effect or provides cover, or through a square occupied by a creature, the target has cover (+4 to AC).

When making a melee attack against an adjacent target, your target has cover if any line from any corner of your square to the target’s square goes through a wall (including a low wall). When making a melee attack against a target that isn’t adjacent to you (such as with a reach weapon), use the rules for determining cover from ranged attacks.

However, note that according to these rules other creatures do not have Cover from a burrowing creature's ranged attacks, only their directly adjacent melee attacks.

Finally, the implications of having Total Cover should be made clear.

You can’t make an attack against a target that has total cover.

Similarly, burrowed creatures do not have line of effect to other creatures while fully submerged, as "line of effect is blocked by solid barriers", meaning that they are unaffected by most spells (unless said spells are cast as a readied action). As a result, any creatures wishing to attack a fully submerged burrowed creature (perhaps to take advantage of their Blinded status) must first destroy or bypass the wall that they are submerged in before targeting them, or ready an action to attack when the burrowing creature emerges.