Looking Over Book of Challenges: Simply Shocking
A pair of ropers wait to launch an ambush from behind illusions concealing magical minefields.
Setting the ropers in zones of magical traps that they both don’t trigger and don’t take damage from is a sensible way of implementing them.
The advice for scaling up the challenge by adding allied bandits with ranged weapons is a good way to make it more threatening. I’d also consider adding a spellcaster capable of restoring any expended traps between encounters.
As I’ve said elsewhere, I’m not a fan of the whole “you can see through the illusion if you know it’s there” mechanic. In this case, I’d change the illusions from solid walls to bars, latticework, etc. to achieve the same effect, with a rough natural texture to the actual walls for the ropers to blend in with.
The text says the illusory walls start 20’ in from either end of the corridor, but the map has them starting 15’ in. This discrepancy is especially odd because the map has 15’ of unused space at the bottom of its grid, so it could’ve been drawn to match the text without taking up more space.
Despite being quite simple and short (less than one page in total, map included), there’s a fair bit to like about this encounter. It’s easy to run, threatens the PCs in multiple ways (direct damage and Strength drain), and shows intelligence on the part of their opposition, since not only are the ropers fully capable of ignoring the traps, but they would have required someone else’s cooperation to set them up in the first place. That last point also means that, even without taking the scaling advice of adding in some allies for the ropers, there’s a clear way to get through the encounter without engaging in combat by tricking the ropers into thinking the PCs are their spellcasting partner(s).
The whole thing is also easy to change, if necessary. I’m not too bothered by the use of standard stock monsters here, since ropers are weird and unnatural enough to fit in as allies or servants of the spellcaster(s) who set up the rest of the situation, but it’d be straightforward to replace them with something else (there’s no shortage of tentacles/appendages/magic effects that pull victims into a gaping maw in either folklore, other fiction, or reality), provided the traps can be adjusted to suit. The physical set-up itself is also malleable (change the “corridor” to a “corner” or a “winding path” that’s actually going through a large room with illusory obstacles, put both ropers on one side instead of making it symmetrical, etc.). The lack of treasure makes sense to me (since the traps would require regular maintenance), but it wouldn’t break things to include the as-yet-unremoved remains of some past victims.
All in all, this encounter gives a lot to work with despite its brevity, and the idea of combining multiple creatures and magical effects in an intelligent way is a valuable one. This is one of the book’s better entries.