Out of the Box D&D Encounters, Series 2, #5 – Spider Mine

Out of the Box D&D Encounters, Series 2, #5 – Spider Mine

June 23, 2017

Inspiration for encounters can come from a number of sources. Common ones are books, movies and other literary or performance arts. This latest one comes from one you might not expect – an old game. Minesweeper. In this case, the field isn’t a logic exercise to reveal where a mine or other explosive device might be. Instead, we will use a natural creature – a spider.

Spiders that are web-dwellers (as opposed to those that are pursuit hunters like Wolf Spiders) often react based on movement in their webs. If the “mine” in this minefield is based on a spider’s sense of what’s in the web, then we have a movement-based logic exercise to avoid a trap. The more a target moves in the “web,” then the faster a mine approaches. This will then create a dynamic puzzle with a built-in trap. If that trap reacts to movement and explodes in a violent enough manner, they may not want it to explode from simply attacking it.

This should have the effect of either forcing your players to think, evade, or reconsider life choices. If the prize on the other side of this trap is worth it, then player characters will risk almost anything.

It should be noted that this encounter requires the Dungeon Master to be very up front with descriptions as well as measures of time and space. This trap/puzzle will behave in very specific ways depending on the number of feet a player moves. It’s reasonable to expect that the faster a character moves within this trap/puzzle encounter, the faster and more reactive the trap will be. This means a DM will have to be vocal in letting the player characters know when (and I mean exactly when and how much) the Spider Mine moves. A DM that doesn’t should expect to find this trap/puzzle viewed as “unfair” by his or her players.

Therefore, whereas I normally insert “Wisdom/Perception” rolls to detect certain things, I would recommend the DM being very open about the movement of the trap, or at least have lower target numbers for the players to roll to detect such things. Otherwise, you may wish to reduce the damage delivered by the Spider Mine so as to give the players the right tension while reducing its possible deadliness.

Environment: Dungeon
Levels: 4-6

Description: Entering this large circular chamber, 90 feet in diameter, the player characters will have their attention drawn to the center of the room. Hanging from the center of the ceiling is a silver-like metal sphere probably four feet in diameter. It is suspended from the center of the ceiling by a single chain, and this chain appears to ascend through the ceiling via a six-inch diameter hole. That hole sits at the center of a five-foot diameter circular door bisected in the middle. This sphere hangs perhaps six inches above the floor and makes no internal noise. It simply hangs silently and motionless.

That is until a player character enters the room.

The second the first step is taken upon the floor, this sphere disconnects from the chain and the chain quickly ascends through the hole in the ceiling. The sphere falls to the floor with a ringing clang. When the sphere contacts the floor, eight metal legs erupt from the sphere equidistant around the circumference of the sphere.

From this point, it is vitally important that the DM and the player characters track each foot moved. For each movement a player character makes, this Spider Mine will move one foot toward them. Should the player characters all stay tightly packed together and move quickly, the Spider Mine will move directly toward them at a ratio of one-to-one for each foot of movement made.

Once the Spider Mine gets within five feet of a living target, it will explode. This will deal 5d6 Thunder damage in a 15-foot radius, but the player characters that pass a DC:15 Constitution saving throw can take half damage. The second the Spider Mine explodes, the doors in the ceiling will quickly open, drop another Spider Mine above the center of the floor in the middle of the room, and await for movement to trigger. The doors open and close very quickly.

This can seem unfair, until the player characters realize the trick. There are a few solutions to this puzzle. If the player characters have some method of walking the walls or ceiling (like with the Spider Climb spell or riding Steeder mounts), this will not activate the trap as the characters are not touching the floor. Player characters also could use the spells Fly or Teleport and not set it off.

Another way the player characters could fool the Spider Mine is by separating as far from each other as they can as they cross the room, and taking turns moving to draw the Spider Mine away from an ally.

If the player characters come up with another solution, it most certainly is up to the individual DM to judge that solution as to whether it’s viable or not.

Attacking the Spider Mine in melee will just make it explode the second a living player character (or other living ally) gets within five feet of it. That will, of course, activate the Thunder damage and the Constitution saving throw.

Knowing how player characters tend to think, for those characters who wish to attack the Spider Mine with ranged attacks, it has an AC of 18 and blows up once taking 25 hit points of damage, is immune to Poison, Charm, Sleep, Exhaustion, Paralysis, and similar conditions associated with a construct. Again, once it’s destroyed, another Spider Mine will appear. If it needs to make a saving throw, don’t over think it and just roll a flat d20. It’s intended to be a puzzle or a trap, not a foe.

If all player characters cross the room and the Spider Mine has yet to detonate, it will return to the very center of the room and its legs will retract.

Monsters: Spider Mines. Hopefully only one. However, if your players are like my players …

Treasure: This trap/puzzle is intended as a guard for some sort of magical treasure. It might be part of a defense for a up to a Rare magical item. This is, of course, up to the DM in question.

Complications: The single biggest complication arises should there be multiple Spider Mines in play, one after the other. That can really add up some serious damage. This trap/puzzle requires the players to think together and come up with unusual solutions. This isn’t something they can just run-and-gun their way through. The DM should offer one or two solutions to player characters that become frustrated. Otherwise, encourage your players that there are actual solutions to problems like these.

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