Looking Over Book of Challenges: Watch Your Balance

Premise

Phase spiders have found an old pivoting-floor trap to help them catch prey.

Good

As ever, I’m a fan of traps that add a divide-and-conquer element to combat by splitting the party forcibly.

The 10’-length for damage on the rising side is pretty sensible (assuming the entire corridor tilts, the geometry gives a height of about 2’-8” there in the raised position, which is right around the lower limit for non-crawlspace personnel access by most industrial standards), though there might be a case for giving a saving throw bonus to very short characters.

The map does a good job of presenting multiple elevations clearly and in a compact space. The only missing information is how much of the floor tilts; I assume it’s the whole thing, but neither the map nor the text is clear about if there is a safe area near the end.

Given how sensitive the pivot is and how shallow its maximum angle is, I agree completely with resetting it immediately after any weight on it is removed.

While it uses far more words than necessary, the tactics for the phase spiders are described well. The advice for scaling the challenge even mentions how to modify the tactics for its suggestions!

Salvageable

The prohibition against driving spikes or pitons into the stonework seems contrived, especially with how 3E typically tries to model everything. I’d make it difficult and vulnerable to getting knocked out or sheared off but not impossible.

The hall ought to have some evidence of the trap, such as scrapes on the walls, rounded or chipped edges on the floor at the wall joints, impact marks on the ceiling and floor, and so forth. Given that the trap trips with just 100 ft-lbs of moment, it’d probably even be reasonable to have it wobble when loaded near the pivot, though I’d favor Hand Waving that away as insufficient to overcome static friction at the walls (since the trap is more about tactical impact than damage).

The floor tilts only to about 15°, which is about the maximum angle for a steep wheelchair access ramp. I can understand it causing characters to tumble down (especially if they’re taken by surprise), but stopping a fall ought to be an easier saving throw to make than the one to reduce the crushing damage on the rising side.

Again, the maximum floor tilt is about the same as a steep wheelchair access ramp. DC 30 to climb it is ridiculous, given that the DC table for Climb describes DC 0 as “a slope too steep to walk up” (i.e. steeper than the actual maximum slope in this encounter).

I’m not a fan of guaranteeing surprise for the phase spiders’ first attack. It should be very likely, sure, but I’d go with 5-in-6 or 35-in-36 (i.e. the 6-in-6 skill check from Lamentations of the Flame Princess) rather than 100%.

I’d make the trap-locking levers each prevent their side from going down rather than having the pivot lock if both are thrown but do nothing if only one or the other is.

Bad

While I can understand simplifying the physics to avoid slowing play for extra math in most game systems, 3E Dungeons & Dragons is exactly the system where it’s fit in, so I dislike reducing the trigger to a matter of just distance from the pivot instead of working with moments. A minor gripe, but it’s one I couldn’t let pass.

The sidebar repeating the rules for fighting while climbing is worthless.

The art shows only the floor right in front of the entrance pivoting, but the side view map shows about four times as much.

The southern levers in areas B are rather pointless, given that tossing a small weight (about 2 lbs) through the arrow slits would be enough to make the floor pivot. Having an old weight on a string would be a better explanation of how the original builders operated the trap safely. There’s also no mention of whether they can be moved independently nor of what happens if both are thrown in opposite directions (if possible).

There’s no information given about the secret doors between area A and areas B.

Almost nothing is done with the lower level.

The advice for scaling the challenge is just about varying the number of creatures.

Overall

This is a pretty interesting encounter. Normal pits, portcullises, etc. might be manageable to overcome by EL 9, so a way of separating characters that seals behind them is a good way to up the stakes, but I could easily see this being used in any situation where the degree of engineering is appropriate (just vary the height of the drop to areas C if increasing or reducing the damage is desired). The abilities of phase spiders make them a strong fit on the creature side, but anything intelligent that can either take advantage of the arrow slits, climb/float/fly freely, and/or move through the walls can work well. Changing the creatures is even somewhat supported by all the tidbits about how the original builders used to use it.

Connecting the encounter to greater context is simple. Make it an obstacle that the players want to go through in pursuit of some goal, add dressing in areas B and/or C that connects to further worldbuilding, tie in its original buildings and subsequent inhabitants with transitions of power in the region’s history; it’s very much a blank slate that can be customized extensively without needing mechanical changes.

The only potential downside is the lack of treasure, but adding in something is easy, whether it’s a light bit of bait partway down the tilting corridor, belongings of whoever’s using the checkpoint, or leftovers from previous occupants/victims (if it’s inhabited by creatures that wouldn’t care much about treasure, such as the phase spiders).

All in all, this is a very cool addition for any engineered fortress or stronghold. It’s too elaborate to be a field modification (unlike No Loose Ends), but it’s not so elaborate as to require mad wizards or some genius designer.