I originally intended to run “Ambush in the Stacks” as soon as the party entered the stacks, before they started looking for a way out, but they seemed worried enough before entering the area at all that I decided to improvise a bit and start the encounter about halfway through the skill challenge. I didn’t want them to run away as soon as things got a little dangerous, after all.
I realized belatedly that the plague spore creatures, though less complicated than the wrackspawn from the first batch of encounters, were still a pain in the butt to manage. Even with one player tracking hit points and another tracking initiative, there was too much to try and keep in mind, and I didn’t like the idea of forcing players to make Perception checks whenever they wanted to attack. (Plus, they had a light source.)
For whatever reason, I can’t wrap my head around the order of events during a surprise round, so I’ll just continue to ignore them. I don’t like having people roll Perception to determine yadda, yadda, bored now. I think I’d just rather have the creatures be invisible so long as they have any cover or concealment. That’s easier than having anyone make opposed Stealth and Perception checks. *sigh*
Anyway, the things that worked with this encounter: the cramped area (fairly small room, lots of shelves) made the creatures’ ability to move incredibly useful. The plague spores could move through the space of Medium creatures and they ignored the “blocking terrain” that the shelves represented to the rest of the party. I was a little sad I didn’t get to dominate anyone, but there will be a “next time.”