Enemies that are good at ambush tactics could be a challenge for this party IMO.
Another way to challenge such a group could be adventure days that have more encounters in them. Having a party with so many casters would be harder to deplete of magic that many, but it could get them thinking about spell conservation.
In a pinch night battles are almost always more difficult than normal battles. I usually dislike using them, but as a very rare event they could shake things up.
If you're running these scenarios for actual PFS credit, then you cannot modify the encounters. If they're having fun, then I see no reason to worry. Some tactics you might be able to use in a PFS event would be keeping the monsters spread out or behind total cover to limit the number of enemies that the players can affect while making effective use of ranged attacks (if the enemies are adequately equipped).
If these are non-PFS events, monsters with SR and high Will saves will make them have to rethink their strategy. A spider swarm (or three), with its immunity to mind-affecting effects, sounds like fun. Sure, they can be dealt with easily with a different spell, but that's one fewer sleep spell they'll have for later in the day.
Most undead are immune to sleep/slumber as are elves if I recall?
It's an easy enough swap to change one monster stat block for another if not in PFS.
Having all of your players using the same one trick pony sets them up for a failure of epic proportions...
Will saves negate this.
It's also going to fall by the wayside at higher levels, unless your party is full of Witches. In that case, enjoy the cackling?
Also, in my experience with APs and modules, level 1-3 encounters can have a pretty gentle curve.
This is good - many feel that low-level characters in 3.X games aren't that consistently good at anything, and failure can be hard to bounce back from.
This is the internet, so I'm sure some will disagree. Either way, I'd say mix it up a bit, and understand that some of these tactics will simply not be feasible as everybody levels up.
Being PFS there is little you can do about encounter make-up.
First read up on sleep and deep slumber and make sure you're not making it easier on the players than is should. At low levels, sleep is a very viable tactic but soon that 4 HD limit becomes a problem. Remember, that 4 HD is total not everything less than 4 HD. Sleep only has a 10 ft. radius, again very limiting.
Double-check the DC of the will save. Unless they've really optimized it there should be a good chance at a save.
It sounds like the group may just be a one-trick pony. Remember Constructs, Dragons, Elementals, Elves, Plants, and Undead are immune to sleep effects. Things might go very badly for them with these types of encounters.
Wounding a creature also awakens it. So they better kill it on the first try. You could also have an awake enemy rouse other enemies.
If this is spoiling other players' fun, you could ask them to tone it down so all may enjoy, but if no one is objecting and they play it by the rules.
Wounding a creature also awakens it. So they better kill it on the first try. You could also have an awake enemy rouse other enemies.
Tis my advice.
Baddy 1 rouses Baddy 2, 3 and 6 on his turn. Then it's on again :)
elves. Move the campaign to the forest and have them deal with elves.