In our D&D 4th Edition campaign, the players have recently encounter Bulettes, monsters with the
Burrow movement mode, and we had a few issues dealing with their movement. Monster Manual 1 states:
Burrow [Movement Mode]: A monster with a burrow speed can move through loose earth at the stated speed and move through solid stone at one-half its burrow speed. A monster can't shift or charge while burrowing.
A monster can't be seen while it's burrowing, but it can be heard...
Also, the Bulette power card states:
Ground Eruption: The squares into which a bulette surfaces and the squares it leaves when it burrows underground become difficult terrain.
This suggests that burrowing involves transitioning between "surface" and "burrowed" states, but the rules do not adequately describe this transition. We came up with two possible interpretations: either burrowing works like phasing or burrowing works like flying.
Option 1: Burrow works like phasing, where the creature gains the "effect" while moving. Any squares moved as part of a burrow have the rules for burrow applied to it, such as not being seen while burrowing. This raises the following questions:
- Can it burrow some squares and not some other squares in a single movement action? For example, can a bulette that is standing on wood, walk 3 squares until it stands on earth, then burrow the remaining 3 squares?
- Does a creature with burrow provoke an opportunity attack when it leaves a threatened square by burrowing? In this case, the question one of when the "burrow" effect starts: does the creature lose line of sight before or after it begins its move?
- Can a creature end its turn burrowed, and thus cannot be attacked unless the attack can work without line of sight or line of effect through solid earth or stone?
Option 2: Burrow work like flying, where Z-axis movement is tracked as the creature descends into the ground. The creature's depth is tracked and burrowing creatures can move above and below each other through the ground, much like flying creatures can go above and below each other in the air. A creature can go out of range by burrowing to a sufficient depth.
This interpretation resolves one of the above questions because each square of burrowed terrain is calculated independently, and burrowing through stone at half speed would be tracked much like moving through squares of difficult terrain. However, it still leaves the question of opportunity attacks unanswered:
- When does the creature go out of line of sight? Is it when it is fully within the earth? Does the first step the bulette take when it burrows take it halfway into the ground, since it's a large (2x2) creature? Does it need to move 2 squares to fully go out of line of sight?
This second interpretation is supported by the Warden power Shake the Earth from the Earth Shaker Paragon Path described in Primal Power:
Close Burst 4
If the target is burrowing, you slide it 4 squares to the square nearest to it that is within your line of effect.
I understand this is meant to allow a creature up to 4 squares deep underground to be slid directly upwards to the surface of the ground. This would force a medium creature 4 squares deep underground to be slid fully above the ground, suggesting that line of effect is only granted once a creature occupies squares above the surface. However, a 2x2 bulette could be partially hit by this power if it were 4 and 5 squares deep underground, and sliding it 4 squares would only take it partially above the surface, presumably now within line of effect and line of sight. This suggests that a bulette could not burrow away from a threatened square without provoking opportunity attacks.
Which movement mode is correct?
Does a non-burrowed bulette adjacent to a player provoke an opportunity attack when it move away with a burrow?
When the bulette burrows, which squares become difficult terrain? If option 2 is employed, would a total of 2x3 squares become difficult terrain as the bulette diagonally moves into the ground?
Can a bulette attack while partially burrowed (1 square deep)?
If option 1: can a creature that starts its turn burrowed make an attack before making a movement to "unburrow"?
Can a creature jump while burrowed? The Bulette's Bite attack grants a standing long jump as a free action; can this movement be made while the creature is burrowed to leap through soil and air alike?
Does a partially submerged bulette need to make endurance checks for drowning? For example, a bulette is knocked into a pool and swims to the bottom of the pool and begins burrowing into the stone containing the water. It ends its turn half in water squares and half in stone squares. Presumably, bulettes can breathe while underground in earth or stone, so it has 4 breathable squares... and it doesn't have tunneling so in strict rules interpretation the water cannot move to fill the squares it burrows through...