Coming back to this, there are a few more snippets of description in the encounter that might help: "The walls are carved in reliefs of tortured faces and bodies fused together into a hideous mass" and "Each interior wall on the map is actually a bizarre magical organism like a cross between a mimic and a stunjelly." The illustration of the walls on the map also reflects the carved body part motif. I'm not sure any sort of stealth ability really fits.
IMO, this shouldn't be a wall that is "
carved into reliefs of tortured faces and bodies fused together in a hideous mass" it should actually be "
made from tortured faces and bodies fused together in a hideous mass".
The wall should have an ability that is an
alternative to creating Burning Zombies. It should be able to skin its victims and use their body parts as part of its outer skin.
I'd even suggest that the armor bonus you mentioned earlier should be a result of multiple layers of leather and hide coverings. If that isn't enough, you could let the creature have an outer layer of unskinned body parts. This would mean that the tortured faces would conceal a layer of skulls and other body parts would have layers of bones below them.
This way, you get a naturally burning ooze that coats itself with its victims to give itself some sort of fire blanket.
To answer the first question, yes, it looks like the object of that encounter is to move through the maze avoiding the walls (and the roaming burning zombies) as far as possible, to get to the exit portals. But from the map, it looks as if it isn't possible to avoid the carnivorous walls entirely, so some combat with a section or two is likely.
If these creatures are slow to move, and if you are giving them the ability to lock together, then maybe they should have group tactics of: creating mazes, waiting for victims to get deep into the mazes and then cutting off the entrances and exits. Once this was done, they could slowly move in for the kill. It wouldn't matter (to the Carnivorous Wall) if they cut someone off and then took two hours slowly cutting off different passages and making the remaining maze grow ever smaller and smaller until the victims
finally realise the walls are alive.
I'd expect the final attack of the Carnivorous Wall would be rather similar to the trash compactor scene from Star Wars!
Interesting. In that case, I say we go with the wall as presented in the adventure, then offer up our "wall mimics" as a variant. The best of both worlds.
If you went with my idea (of coating its body with its victims) you could create a variant Carnivorous Wall that seeks out and kills mimics. Each mimic it kills, could allow it to swap an area of hide/bone armour with an area of surface that has the same qualities as a mimic. When it has killed enough mimics, it could totally get rid of any flesh and bone coverings and have a total surface area that is hard to spot.
I would suggest that any Mimic Carnivorous Walls loose some of that armor bonus when they gain "mimic skin".
(I'm loving your work, BTW

)