I've heavily modified Three Faces of Evil to suit the high-powered needs of my gestalt party, and they really seemed to enjoy the results. So I thought I'd share...
For future reference, here's my party:
Khalavas - human barbarian/bard 5
Kellen - human ninja/cleric of Nola 5
Quince - human wizard/warmage 5
Darion - human knight/fighter 3 (party cohort)
First of all, I scrapped all of the plain vanilla, classless grimlocks, replacing them with two varieties of gestalt grimlock (grimlock elites, as I called them): there were the archers (ranger/fighter 1) and the mashers (barbarian/rogue 1). I added a fiendish five-headed hydra to guard the entrance, along with three mashers in the next room. The party handled them all fairly easily, though the hydra gave them a fun scare.
I restatted the grimlock beastmaster as a druid/ranger 4. The beastmaster had a fleshraker dinosaur for his druid animal companion and a swindlespitter dinosaur for his ranger animal companion (both from the MM3). The beastmaster used fog cloud and his blindsight to split up the party and perform guerilla tactics on them, but he rolled terribly on his attacks and didn't last very long once they cornered him.
The grimlock barbarian became a gestalt barbarian/fighter 3, but she pretty much maintained her original set of tactics in the horseshoe tunnel. I gave her Tunnel Runner and Tunnel Fighting (Underdark feats), and made the horseshoe tunnel even narrower so the PCs would be squeezed. That fight was a little bit tougher, largely because the party was split up (Quince and Kellen failed their Climb checks and fell to the bottom of the cavern, where they tangled with a pair of shadow chokers while Darion and Khalavas fought the barbarian in the tunnel).
At the rope bridge, I used a masher and a pair of archers to stall the party and make them use up some buffs - they were able to force these grimlocks into a retreat fairly quickly, only to run into them again in the cliff chamber.
I restatted the grimlock chieftain as a barbarian/fighter 3 and then added the gravetouched ghoul template. He was accompanied by a pair of ghasts as he came at the party while they were in the middle of their battle with the surviving grimlock elites. That encounter was particularly tough, and they rested shortly afterwards.
Which is good, because I pulled off the kid gloves for their fight with Grallak Kur. I opted not to make him gestalt so I could give him more levels of cleric without raising his CR. I also gave him the voidmind template (his personal history in my campaign has him as a former mind flayer thrall who broke free of his psionic bonds and slaughtered his masters, freeing his clan in the process and proving that he was a chosen prophet of Erythnul). Grallak Kur's final build was voidmind grimlock cleric of Erythnul 7. I gave him the Madness and Trickery domains. I also ruled that his beholder eyes effectively gave him regular eyesight in place of his blindsight, because Kellen hadn't been able to get in any sudden strike in a while and I knew his player was getting antsy. Finally, Grallak had Extra Turning, Quicken Spell, Divine Metamagic (Quicken) and a nightstick in his inventory, which allowed him to quicken a few of his high level spells.
When the party arrived in the Temple of Erythnul, Grallak won initiative and opened up with confusion - Quince and Darion both failed their saves, and were effectively out of commission for the entire fight. This left Khalavas and Kellen to face Grallak Kur alone. Khalavas approached the grimlock's perch first, and had to endure a hold person and a quickened wrack (he made both saves) before Grallak put up divine power and waded into melee. Kellen was able to hit Grallak with a throwing star, prompting Grallak to use his cone of slime on the pair of them. They both made their saves, but still took a crapload of acid damage in the process. At this point Grallak executed a full attack on Khalavas with his morningstar and tentacle; when all was said and done, Khalavas had two hit points left and was being grappled by the sentient tentacle. Kellen then healed him, so Grallak smacked Khalavas with a touch of madness, dazing him for the rest of the battle. This left Grallak Kur and Kellen alone, and Kellen was continuing to use ghost step to remain unseen. Grallak decided to mop up Quince and Darion at this point, since they were wailing on each other at the edge of the battlefield, but Kellen managed to toss a tanglefoot bag at the grimlock priest, who promptly failed his Reflex save, becoming glued to the floor. Kellen followed this up with a round or two of extremely lucky Rapid Shot shuriken-tossing, killing Grallak just as his last use of ki power was exhausted.
Overall, I was quite happy with how everything turned out.
Sounds like you really upped the ante for your players. Kudos! My PCs sort of walked through this section after suffering near back-to back TPKs in the Hextor Wing, so it's cool that you've made the difficulty equal to that section. Good luck with the Aspect!!
Thanks. They still have the temple of Vecna to go through before they face my upgraded Ebon Aspect (I'll post stats later).
I also changed the Vecna temple quite a bit - I removed all of the stock labrynth denizens, replacing them with a pair of gauth beholders. I added an upper level to the labrynth, accessible only to creatures who can fly (and its various vertical entrances are concealed by permanent images). This second level is primarily for the beholders, of course. I am also adding a series of specialized wall of force traps that trigger when any non-evil creature passes over them, or when they are targeted by a beholder's eye ray. These walls of force last for one round, but have an automatic reset. I will use these to cut the party in half (or quarters) as necessary, and hopefully infuriate them.
I'm still not sure what I'm going to do with the Faceless One. I am thinking either wizard 7 or wizard/cleric 6, with no templates. He needs a physically powerful bodyguard or two, either way. I've heard too many stories on these boards about how he gets cornered in melee in the first round and creamed. His acolytes will probably use their scrolls of web to slow down the party, followed by stinking cloud from the Faceless One if possible. I was thinking about how fun this combination would be - anyone who fails both saves will basically be screwed, since nauseated characters can only take a move action, and the action required to escape a web is full-round. And since the allip is incorporeal and undead, it can glide through both effects effortlessly, sapping Wisdom left and right.
Fun!