Whispering Way Stronghold - enemy suggestions

[ArchLich]

In the campaign I run, the group is currently on their way to assault a stronhold of the Whispering Way somewhere in the wilderness of the River Kingdoms. The cultists have subjugated/allied themselves with a group of bandits also operating in the area.
Now, I am looking for suggestions as to what enemies should the players face...not stats-wise but to make the encounter(s) varied and challenging. Usually, I do not have this problem, but I have thrown the usual undead at them already and am looking for something else (maybe templated monsters etc) that will still fit with the Whispering Way.
The group's level is 12 but due to an excellent grip on tactics and beautiful teamplay (really, as frustrating as it is to me as a GM sometimes, they have turned working together to devastate vastly more powerful enemies into an art form) they are easily able to take on CR 14 and 15.
So, any suggestions would be very welcome in regards to enemies - or other features that might be interesting.

[stack]

CR14 may make this moot, but at lower levels I had fun running a gravetouched ghoul (ghoul that keeps class levels, from 3.5), with a tripping monk build. Paralysis with claw attacks and stunning fist meant for lots of saves.

Juju-zombies are PF-native and keep class levels, so undead any class works out there. Sorceror's and oracles are nice since undead benefit from high CHA.

[ArchLich]

Okay, sounds interesting...other thoughts? Specific monsters that would be a good fit? Don't have to be undead if they'd fit.

[Sayt]

Daughters of Urgathoa (http://www.d20pfsrd.com/bestiary/monster-listings/undead/daughter-of-the-dead) with cleric levels, Ghouls/Ghasts with monk levels, Agents of the grave (http://www.d20pfsrd.com/classes/prestige-classes/other-paizo/a-b/agent-of-the-grave), Skeletal Champions, Zombie Lords are all extremely appropriate choices for a Whispering way Hideout.

For the dungeon boss, if they grab a level or two, might I suggest an Awakened Demilich (http://www.d20pfsrd.com/bestiary/monster-listings/undead/demilich/demilich-awakened)? (It's treasure, of course, being the minions the PC's have been slaughtering.)