Friday, November 9, 2012

More Interesting Traps: The Boulder Trap

         The boulder trap is an trap that presents an encounter all by itself. It tests a number of different skills and abilities, as well as the PCs’ decision making process. It also presents the PCs with a goal very different from the usual fare: Running away.

         PCs are a reckless lot, by birth. They are used to winning fights and succeeding at tasks. Retreat is a situation that they rarely find themselves in. The Boulder Trap provides our heroes with an opportunity to stretch their legs, and get running.

         The Boulder Trap is intended for parties with an APL of six through eight, but it can easily be adjusted to heroes of any level.

         The Boulder Trap consists of three consecutive hallways which the heroes are encouraged to navigate as quickly as possible. These three hallways are filled with a number of obstacles to a straight and unhindered flight: enemies, difficult terrain, and pits. A boulder rolls after the heroes at a speed slightly below what the heroes can manage, a pace that encourages them to hurry.

         The trap takes place inside initiative order, and a few small fights are possible as the boulder rolls. Make sure to keep track of initiative and keep track of the boulder’s place in it.

The Trigger

         The boulder trap would be no fun if it didn’t go off. However, a character with a high enough disable device check can dull the mechanism and make the trap easier to navigate. The trigger consists of a wall of nearly invisible wires forming a complex spider web. It is impossible to move through the hallway without triggering these wires, unless the entire party has the ability to go insubstantial or teleport. The perception check to notice these wires is 25. The wires don't block movement, and if somebody moves through them the trap goes off.

         A character with a disable device check can attempt to disable the wires. There are 10 key wires, and if he can disable them all, the trap does not go off. The character notices that each wire is more difficult to disarm then the last. The first wire has a DC of 10, then second has a DC of 15, the third has a DC of 20, etc...

         When the player inevitably botches one of his disable device rolls, explain that he disabled some number of wires, preventing the trap from working fully, but he accidently tripped the wire he was working on. The trap should then begin. When the trap begins, a secret panel opens up behind our heroes and the boulder comes sliding down 20 squares behind the trigger. Place the boulder at its starting position, and roll initiative. Explain that the boulder has started to roll at the heroes.

         However, the character’s disable device check was not for naught. For every wire that the PC successfully disabled, reduce the boulder’s speed by five feet. Explain that the panel did not deploy correctly, and that the boulder lost some speed as it rolled down.

The Boulder

         In many ways, the boulder can be treated as an "–" intelligence monster. The boulder has no actions other than moving each turn. It moves 10 squares each turn (if no wires were disabled), ensuring that if characters want to stay in front of it, they had better run, double move, or have enough leeway that they can deal with an obstacle before being crushed.

         If the boulder enters the same square as a character, it elicits a 25 DC reflex save. On a hit, the boulder deals 12d6 +10 bludgeoning damage to both the victim and his armor and knocks the victim prone. On a save, it deals half damage to both the victim and his armor and knocks the PC prone. Either way, the boulder continues on its path completely unhindered.

         The boulder can be attacked, but it is immune to slashing and piercing damage and takes half damage from energy attacks (fire, ice, sonic, etc...) and full damage from force attacks. It has 120 health. For every 20 bludgeoning or force damage that it is dealt, it’s speed is reduced by five feet. If the boulder is reduced to zero damage, it simply falls apart. It has no reflex or will save, but it has a fortitude save of +20 and an AC of 5. The boulder has an initiative bonus of -20.

         It should be noted that the corners and ends of the hallway are slanted, such that the boulder will turn and continue with the corridor.

The Hallways

         The trap consists of three hallways that the heroes are chased down, each hallway being 24 squares long, or 120 feet. There are a number of obstacles to avoid in these hallways. In the first hallway, there are no real obstacles – just the trap trigger and an empty place to run. This is to get the PCs acclimated to the idea that they are running away from the boulder.

         The second hallway will present more of a challenge. There are two enemies in this hallway – one near the start of the hallway, and one near the rear. Each of these enemies should have a CR of 3, be small or medium sized, and should be dungeon appropriate. An Advanced Draugr will do for most dungeons. These enemies should not be difficult to dispatch. However, killing them takes up valuable time and will slow the PCs down, while running past them will incur opportunity attacks.

         In the center of the second hallway there is a 30 foot long rectangle of difficult terrain spanning the length of the hallway. This terrain could be a partial cave in, slime on the ground, a broken statue – it doesn’t matter. What does matter is that it will slow our heroes down.

         Immediately at the start of the third hallway, there are two bear traps that are chained to the ground. These will both deal players damage and restrain them, eliciting a disable device check, escape artist check, or strength check. If the bear traps are noticed, they can be easily avoided without a check of any kind.

         In the third hallway, there is a shallow pool of water that stretches 30 feet down the corridor. The pool acts as difficult terrain. However, because it is flush with the ground, our heroes may attempt to long jump across it. They probably won’t make it the full 30 feet, but every square they jump is another square they don’t have to move through difficult terrain.

         Near the end of the third hallway, there is a monster with CR 4, such as a Minotaur. The monster should be dungeon appropriate, and it should be large and take up the width of the hallway, meaning that if the heroes want to move past it, they must either kill it or tumble through it.

         At the end of the third hallway, there is a ten foot wall leading up into the next room. The wall has a climb DC of 20. This wall is the final test. When the boulder reaches the wall it will crash harmlessly, and can go no further.


  1. I quite like this, and will use it. Thanks!

    Doug M.

  2. What XP would you give this entirely awesome trap?
    Bear Traps x2 + Derro x2 + Minotaur = CR 7 3600
    The various Skills used (DD, Climb, Perception) and the Boulder? Maybe add another CR 3 for this combination.

    Total XP for a level 6-8 is a CR 7700. I think that's super fair and fun.

    1. Good question! I don't give out exp anymore (blog post forthcoming), but just for the sake of things, I'd put this at about 3,500 exp, for getting through it, +600 if the minataur is killed and +400 for each Draugr killed. I don't want to reward killing the monsters too much, as the point is running away. That's 4,900 if they kill the baddies, or about CR 8.

      The actual difficulty for the party will vary significantly though. For a party of all ninjas, barbarians, and teleporters, this will be a cake walk. Throw in some heavily armored halflings or a lame oracle, and you've got potential death on your hands.

      If you run it, let me know!

  3. And when the GM tells the players to roll initiative, they must put this music on a continuous loop until the trap is passed: