Need Monster Selection Advice

[bojac6]

Hi, so I'm running a long running game with 6 characters (and a badass wolf companion) that has gotten into the high levels (16-17) and combat has become a slog and a chore. So I'm spicing things up by making encounters very non-traditional, to keep them interesting.

Currently, they are after a list of documents secure in a powerful devil's library. In order to get the documents they will need to unlock the shelf. Unlock consists of doing the right type of damage, depending on a symbol. So they see the symbol for bludgeoning, force and fire, and they do those damage types to the lock in the same round it to unlock it. Then somebody gets access to the document, reads it, and they move on to the next one.

What I want is for them to be underattack the whole time by a lot of minor, but still threatening enemies. Basically, I want them to have to think "Ok, we need 4 characters to hit it with damage, but we also need to clear some space, so all of us spend a round clearing the area around us to buy time for 4 of us to open the lock while only 3 of us are fending off the baddies." I don't mind them slowing down to discuss the strategy at the table, in fact I want that. There's enough role play in the group that even with them playing tactically, there will be tension and engagment.

So my question is, what should these waves of enemies be? I mean I can flavor them however I want, no problem there, but what makes an enemy threatening enough that you want to deal with it, but easy enough to take out quickly. I don't want this to turn into another slog against some tough enemy with a thousand hit points, but I also don't want it to be something they can just ignore. My gut says something like a ghoul, but with the save versus paralysis really cranked up so it's tough.

Any good ideas, suggestions?

[Goth Guru]

The librarians are damned wizards with their eyes removed. Basically petitioners that are solid, regenerate daily, have fast healing 2, except their eyes. They keep coming, following the noise, and trying to steal character's eyes. Any spells they cast, they can never rememorize. You might give them minor wands or bone knives.

[SanKeshun]

Set up a horde of small, easy-to-kill devils. Basically just evil knowledge-spirits that don't have enough power to become a full devil. However, they have a special attack:

Knowledge Spike (Su) A Knowledge Devil can attack a creature's mind directly, bypassing all defensive magic and items. They make a single attack roll against a foe withing 15 ft., using the target's Intelligence score as AC and the appropriate Knowledge skill bonus in place of their normal attack bonus. If this attack hits, it deals 1d6 points of damage, and the target must make a DC 19 Will save or take 1 point of Intelligence damage.

So, is it deadly? No. It's a nuisance. But over a few minutes of wandering through a library with a small hoard of the things showing up all the time, attrition becomes a consideration. The challenge is not in the fight, but in how to deal with the inexorable drain on hit points.

[SanKeshun]

Although, now that I think about it, you can accomplish the same thing with a single devil with, say, 200 hit points? Just give it a good attack bonus, bleed damage, and a simple curse: the bleeding wounds cannot be closed until the curse is dispelled.
The devil is killed swiftly, but it'll be able to inflict a good deal of bleed damage. The PCs waste a few spells or magic item charges getting rid of the curses, and heal themselves back up.

Then put one of these devils guarding every shelf, with several wandering around stealthily as well.
I wonder how many curses the party can dispel before they get into a race against time with their swiftly-depleting hit points...