Horned Devil together with 2 Barbed Devils (according to the DM there was actually a larger number of foes listed, but he scaled that down, since they got a bit tougher in 3.5 (CotSQ is 3.0)... Oookay CR 10 -> CR 16 is a bit more than just "a bit" tougher and the Horned Devil is a real meanie now! It also turned out to be that tough. The Horned Devil lobbed Fireballs into the melee where our Paladin and Barbarian tried to bring down the second Barbed Devil (the other was blinded from my Glitterdust and pretty much out of the game), which luckily succeeded after a few rounds, and afterwards the big demon headed for my Sorceress (who had a Greater Blink up, but still had to Dimension Door away after two rounds (thanks to my over 100 hit points with False Life that was still possible) and a lucky save against the stunning only to find out that healing potions do not work with the Infernal Wound, so it was another empowered False Life and back to the fight. As expected, things went down fast and we had only so much as scratched the big one yet. Anyways, by then the Barbed Devil were both dead and the Horned Devil now in melee with our heavily wounded fighters... only a wonder could save us now and it came after few rounds when the Paladin hit for 60 points total and the Barbarian critted a full Power Attack strike for a whopping 80 damage with his bastard sword (not such a bad feat against the mid thirty AC)! That round the so far only slightly wounded devil went down and was then systematically hacked to pieces with a Blessed Weapon (fortunately, the DM forgot about the silver part and so the DR was breachable by a good-aligned weapon as we later realized, but that was probably just fair enough ;-)).