The skulks were tough to make challenging, given how much weaker they are than the party. Their stealthiness and ambush strategy helped, but mostly I wanted them to keep the party busy while the big hitters, the golem and the taiga giant, came in to be the actual threat. And then circumstances intervened to ruin my plans. To start off, they missed every single one of their shots in the first ambush against Milacent coming down the stairs. I rolled four natural ones in that fight, and had to switch to another d20 for the rest of the session. Then I just straight up forgot about the taiga giant until the fight with the next group of skulks was just about over. It’s probably because it starts in another room, and I was intensely focused on the two rooms the skulks would be staging their double ambush from.
That said, the fight still managed to be somewhat interesting. I never expected these guys to be able to stop the party, but taking down one of their charmed servants means there’s still some level of challenge in the adventure, which is a good thing. In the Paizo forums, people complain about a lot of the Adventure Paths being too easy for optimized parties, and I’m certainly seeing some of that here. Unfortunately, the solutions they offer often involve a lot of messing around with the rules: giving monsters double or triple hit points, giving bosses extra actions, etc. I’m not going to do that mostly because it breaks the GM/Player contract as I’ve always understood it: the players agree to the GM’s rulings and the GM in turn adjudicates the rules as fairly as possible. As my players know, I actually quit a campaign once when we discovered the GM was handing out 1/3 earned experience.
So how do I adjust difficulty? Tactics is one thing. These Paizo adventures sometimes have the bad guys use really poor tactics, presumably to make things easier for weaker parties, but this party doesn’t need that kind of coddling. Of course, the giants still just charge straight ahead, because they’re giants and they’re stupid.
There’s also enemy numbers. Some of the old TSR modules wouldn’t give set numbers for enemies, instead giving a ratio such as ‘two for every PC’. I haven’t seen that in Paizo adventures, but I think it’s fair to increase the number of bad guys in order to make a fight a challenge. I’ve done this very sparingly, but I’ve done it, although now that I think about it I can’t come up with a time that I’ve done it in this particular campaign. It’s something I would use to make a climactic final battle more interesting, but I don’t do it in the speed bump battles that often fill a dungeon. For those I prefer to have creatures hear nearby fighting and join in, so that instead of lots of little, boring fights we have one, relatively epic fight. You saw that in this session.
The last thing is enemy force composition. If I could do the Lady’s Light adventure again I would make the fake Sorshen more formidable, or at least have her accompanied by bodyguards, in order to make the fight with her less anticlimactic. This is the hardest one because it takes planning, and the whole rationale for using published adventures is I don’t have time to plan, but sometimes it’s the best thing. It also requires a fair amount of system knowledge, but if you’re running a game you need that anyway.
All in all creating an appropriate level of challenge is more of an art than a science. I doubt I’ll ever be 100% satisfied with the way it goes, but I do try to hit that sweet spot more often than not. It also helps if I don’t roll a bunch of natural ones.