Remember what I said about my concerns that they would go outside the box enough to break what I had planned? That didn't quite happen, but it very nearly did.
CR20 encounter w/ 2 level 10s and a level 9, played with some abilities locked but with specific other ones added in. Maximized the HP of the foe. Gave her a weapon that does an additional 1d4+2 Dex damage on hit and instantly shatters non-artifact level weapons on successful parry/sunder attempt. The players fought tooth and nail to win the encounter and very nearly did(I had a backup plan for the main villain's general to show up if she lost the fight, but I didn't want to have to use it).
The main heroes and an NPC ally(Samantha) enter the fortress and face off against an Evil Eye, the same type of foe that the cohorts faced in the last adventure. It manages to bloody them a bit, mostly through use of its Flame Strike gaze and some high rolls on the damage dice. Proceeding on, they manage to avoid the rot grubs. Poor pit placement(really, its just an over-reliance on them causing there to be no path that anyone can travel and not end up adjacent to a pit) and difficult terrain(the floor was slick with gore) nearly spells the end for Samantha during the encounter with three Leukodaemons. Obrek gets bloodied as well.
They had a little trouble destroying the first control orb that shielded the adamantine door leading towards the throne room. I was using it as a bit of foreshadowing, so it wasn't smashable via normal means. I kept mentioning that it was evil and shielded against normal attacks, but they weren't quite catching on that they had to use either some kind of holy attack(Lay on Hands, Smite Evil, holy water) or something that bypasses normal protections(Gribbletoo's scythe does divine damage and is not subject to any form of DR or resist on any of its attacks; could also summon Lantern archons to bypass the protections). Eventually had to have Samantha start helping Obrek in attacking it, and she chastised Gribbletoo for not helping as well since it was taking too long.
They head down the other wing and find some prisoners, who tell them that the Leukodaemons are infecting people with some kind of disease. One of the prisoners is a cleric, who recognized some potions in the next room as Remove Disease potions. The players head into the next room and find another Leukodaemon infecting a prisoner. Nervous about the difficulty of their fight with the three of them, they blow far too many of their resources on the single enemy encounter. They then cure the prisoners of their diseases and shatter the second orb.
When they return to the entryway, they find the door open and a pair of evil eyes. The use of resources on this particular encounter was justifiable. Due to some bad luck on her part(I rolled the targets and spell effects of the attacks randomly), she eats two Flame Strike gaze attacks simultaneously and once again is nearly killed. Players blow a fair ton of resources bringing the foes down.
Finally, they reach the throne room and are faced with a woman looking like a swashbuckler(really Astaroth in disguise). In round two, the ground shakes and its revealed to the players that their cohorts just blew themselves up(see post for last adventure). I activate a certain house rule(Limit Breaks) and give them back some of their daily resources. For Obrek, a charge of Smite Evil. For Gribbletoo, some charges on his Scythe/staff are replenished. They deal a fair bit of damage in round two, but Obrek and Samantha are both hurting, with around 6 dex damage apiece.
In round three, I shatter both Obrek and Samantha's weapons(a sunder and a parry, respectively) and knock both paladins into 0 Dex. Gribbletoo goes into panic mode and starts pulling out all the stops. A pit, several Ball Lightnings(divine damage as they were conjured via the staff) and multiple summoned monsters later, he finally goes down. Took 6 rounds to pull it off, thanks to some poor rolls on the villains attacks and saves. Astaroth was down to around 20 or so HP remaining(of nearly 300).
The characters watch helplessly as the villain prepares to use the blade to devour the soul of each of them in turn, starting with Samantha and gloating the entire time. She's struck by an arrow and Falric arrives, Veil and several paladins in tow. He tells Veil to get the heroes out of there. She uses her teleportation amulet to get the three injured people and herself out. The heroes pass out from their wounds and awaken almost a week later in a healing ward in the Temple of Iomedae. Falric never returned and Obrek no longer feels Iomedae's presence in the temple.
Now I need to set up the next adventure, which is basically Mt. Ordeals from FFIV. Since the one roommate is visiting family this week and won't return until next Sunday, I'll have two weeks to plot it out. Which is good, since I have no idea how to stat up Astaroth's fiendish earth themed general.