Leander did a good job describing the issue, but since I love to over-clarify, here's the relevant text:
KK, p.2
Giant Stone Boulder
The giant stone boulder rolls down
a corridor, doing great damage to
anything in its path.KK, p.6
When the last Hero passes the square marked "A", a giant
stone boulder will fall from the ceiling. Place the round
boulder tile on the square marked "A". On your (Zargon's)
next turn and subsequent turns, roll 2d6 to see how far down
the corridor the boulder rolls (to the right, toward the
Heroes). The boulder will eventually crash into the wall at
the end of the passage, on the corner square marked with a
starburst. The passage will then be blocked for the rest of
the Quest. Tell each Hero hit by the boulder to roll 5
Combat Dice. For each Skull rolled, a Hero loses 1 Body
Point. (No Defend Dice are rolled.) the boulder trap
cannot be searched for or disarmed.How I think it works:
- The last Hero passes "A", finishing any remaining movement.
- On Zargon's turn the round boulder tile is placed at "A"
- On the Heroes's next turn and subsequent turns, they all may move and take an action.
- On Zargon's next turn and subsequent turns, the boulder moves 2d6 squares to the right.
- If the boulder moves onto a square with a Hero, the Hero rolls 5 Combat Dice and takes damage for each Skull rolled. Continue moving the boulder to the right if there is any movement remaining. If the boulder has no more remaining movement, place it under the Hero. In either case, the Hero may no longer move through the boulder, even if he is pinned for a turn (should the movement of the boulder end on him before continuing on Zargon's next turn).
- Multiple Heroes may be crushed by the boulder.
Notes:
1. Most if not all of the Heroes would be crushed if they all passed "A" on their first turn of movement and you allow the boulder to roll just after the last Hero passes "A". The square marked "A" is the third after the entrance door, so all the Heroes would have to have moved at least 6 squares to be just beyond the minimum move of 2 squares by the boulder. If the Heroes all rolled an average of 7 for movement and had to stack behind each other, the boulder would reach at least two victims. More likely an average roll of 7 for boulder movement would crush all the Heroes, unless one or two were lucky enough to roll an 11 or 12 for movement. This suggests the trap shouldn't be started rolling until after the Heroes' second turn of movement. The tension can then be stretched out as the boulder closes in on stumbling Heroes.
2. The odds are better for the Heroes if at least one of them doesn't pass "A" on his first turn by rolling a 2 or 3 for movement. It's also possible one Hero will remain at the entrance doorway to search for traps or secret doors, thus providing more distance for all the Heroes when he passes "A" on his next turn. As these possibilities aren't too likely, I'd say the trap wasn't intended for the Heroes to counter it in this fashion.
3. The boulder needn't interrupt the last Hero's movement and be dropped immediately as he moves 1 square beyond "A". Passing "A" includes his full movement, then place the boulder tile. Of course you could place it immediately for dramatic effect, but it doesn't change the mechanics of the turn sequence. First, the last player who passes "A" finishes his movement, then the boulder is placed on Zargon's turn. This works like a Gargoyle trap that is triggered by opening a door: first the Hero triggers the door/Gargoyle trap, then the Gargoyle attacks on Zargon's turn.
4. Interpreting what constitutes "On your (Zargon's) next turn" is critical to determing when the boulder starts moving towards the Heroes. I maintain Zargon's "next turn" is not on his turn that follows, just after the Hero's turn who last passed "A". Instead, first there is an assumed Zargon turn for placing the boulder tile on "A", where it is redundant and misleading to apply a "next" modifier. Rather, "On your (Zargon's) next turn" more accurately and meaningfully indicates two Zargon turns after the turn that the last Hero passes "A". If this wasn't the case, the Quest note should have been worded more restrictively and clearly: "On your (Zargon's) turn and on subsequent turns, roll 2d6..."
5. The p.2 description describes the boulder as doing great damage to anything in its path. That suggests a squishy obstacle won't prematurely stop it. The p. 6 description states that the boulder will eventually crash into the wall at the end of the passage. Even if a Hero is caught under the boulder, it simply continues it's inevitable movement to the corner location marked with a starburst. Also, if it is big enough to seal a corridor off, it is big enough to roll over a person. The corridor must somehow be widened halfway up the walls to allow the diameter of such a large boulder to fit and yet block a corner. If it were instead small enough to fit in a 3 1/2 foot wide corridor (scaled to the figures), any Hero but perhaps a Dwarf could be expected to leap over it. Besides, everybody is thinking Indiana Jones size anyway. This isn't Mercenary Quest, it's Hero Quest, damnit!
6. Has anybody ever tried a Pass Through Rock spell to avoid this bad boy?