This wasn’t a great session, mostly because I was moving and didn’t have time to prepare properly. Zolerim in particular should have been much more difficult, but I didn’t go through his spell and item list beforehand and think about how he would fight; I just read his stats and made things up on the spot, which works okay for fighting types, not so much for spellcasters. I don’t mind so much because the party had just gone through some tough fights with the qlippoths, so it was time for a relatively easy encounter, but Zolerim’s a fairly major supporting character, and he deserved better.
Pathfinder/3rd Edition D&D is a medium prep system. You can run it without extensive prep, but things will go much better if you work out the more complex things beforehand. No, you cannot predict and plan for every eventuality, but you can identify the more likely possibilities and think about what will happen, especially when you have characters with complex webs of spells and feats. Not only will this make things better when the players do what you expect, it’ll also make you more capable of adapting when things go off the rails. In RPGs as well as many other things, plans are [mostly] useless but planning is indispensable.
Unless you’re busy; then just wing it.