Looking Over Book of Challenges: Formidable Opposition
A ragtag band of creatures tries using a mundane mirror and magical mimicry to trick the party.
The doppelgangers needing to approximate the party’s weapons with the ones they have available is a nice touch for hinting that something is amiss.
The NPCs have a few couple interesting potions among their possessions.
The explicit mention that the creatures will flee when things start going poorly minimizes how long the players are insulted by this terrible encounter.
This encounter is pretty much just a forced combat in an empty room, with the sole distinguishing feature being an initially-hidden mirror that hides a weapon rack. Putting something, anything, in the room that might interest the players could give them a reason to enter would be a good idea.
The second boxed text is misleading. The mirror doesn’t appear “where the wall opposite the door used to be”, it’s revealed when a section of wall disappears.
The text for seeing through the disguises mentions situational adjustments to the DC and to the players’ rolls. I’d treat the -2 DC penalty as a +2 bonus on the roll to keep all of the modifiers on one side of the equation.
The intro suggests locating the encounter along some critical path so that the PCs “need to go through this room, rather than just closing the door and taking a different path”. This doesn’t set good expectations for what’s to come.
I understand the basic set-up here (an illusion of a wall is hiding a big mirror and the four NPCs), but there are so many flaws with it. Using the rules as written, the spell effect called out (illusory wall) can’t actually cover the whole mirror (the mirror is 15’ wide, while illusory wall has a 10’x10’x1’ volume), nor can it be dismissed at will (the duration is permanent and lacks the dismissible tag). The illusionist is supposed to cast some spells to prepare after the PCs enter, but all three of them have verbal components and the illusory wall does nothing to block sound. The second boxed text says the figures materialize in front of the mirror after the illusory wall is dismissed, but both the NPCs and the mirror should all appear at once (unless they cast invisibility spells on themselves and coordinate dismissing those, though that would obviously mean even more preparation time). I know a lot of that can be smoothed over by just not using a game system as rigorous as 3E, but it’s inexcusable for a published encounter to not work (in terms of mechanics) in the game system it was written for.
I may be missing something from relying on the 3.5E SRD, but it seems there’s a case to be made that doppelgangers can’t mimic clothing/armor/etc., which would render this encounter even more unplayable by the rules as written than it is already.
The crux of the NPCs’ tactics is to try tricking the players by appearing like copies of the PCs. Aside from encouraging the GM to cheat (by having the illusionist and efreet focus on using spells they have in common with the PCs they’re mimicking), this seems rather flawed because it counts on the PCs having special defenses against their best tactical choices, which is one hell of an assumption to go with.
The advice for scaling the challenge is combination of the two most useless categories: varying the number of creatures and altering levels/HD.
This encounter is awful, and not just because it doesn’t actually work with the rules it was written for. Infiltration-based creatures (like a doppelganger or a rakshasa) should pretty much never be used as throw-away filler, just as something like a ghost or a Nazgûl-Expy shouldn’t be used like that. These are creatures that should have a purpose for targeting the PCs, that should spend time and resources studying them to improve their mimicry, and that should at least have the potential for a dramatic moment when the deception is revealed. Instead of any of that, this encounter has a handful of dudes sitting in an empty room for no better reason than to half-assedly copy and then ambush whoever comes in. It’s just dumb.
All in all, the only good thing to take away from this encounter is a sterling example of what not to do.