Basically, can a Spider (or any future model with a similar "ignore terrain" special rule) end its move on traditionally unscalable terrain?
Rulebook P28 wrote:
[...]any surface that is sheer (such as a fortress wall) or where we cannot balance a model without the risk of it falling off, cannot be climbed.
Shelob and Spider Queen Entries wrote:
[Spider Mama] can move at full speed over any type of difficult terrain and ignores all obstacles [...]
Giant Spider Entry wrote:
Giant Spiders can climb on any surface, regardless of angle. Giant Spiders can therefore move at full speed over any type of obstacle [...]
What this seems to suggest is that you can send Giant Spiders up a wall and leave them there untouched by your opponent until you're good and ready, but I'm not sure about the heroes. They don't have the "climb on any surface, regardless of angle" specification. Intuitively, it's a spider, it can. Read as written, how would you rule it?
This came up when I did exactly that, hid my Shelob up a big rock wall for a few turns until Dain was busy, then she got in.