well, they decided against Tyrus. Probably a sensible course of action, though they are still interested - maybe with a couple more levels under their belts.
So they decided to hit Thorodin in region K instead.
They buffed themselves through the hilt including fly and haste on the two fighters and fly and greater invisibility on the two rogues, water walking on the rest and water breathing all round just in case. Heroism on everyone as well.
They ran / flew across the water from the northern entrance to Pyrefaust, taking about 3 rounds to get to Thorodin, who saw them coming and started buffing the toadies before flying up to get the option to crush on the flying fighters.
All party members failed their saves versus frightful prescense, but that just cancelled out the heroism.
3 rounds later he was dead. A critical from the axe wielding Eldritch Knight and hits from the fighter, coupled with successful sneak attacks from the rogue and assassin and he couldn't handle the damage. He did get a breath off and had the EK running away right at the end of the fight (saved by stoneskin and energy resistance - acid), but even so it was done and dusted before the Greater Invisibility ran out. The sorcerer torched all the toadies with a single fireball, rolling so well with damage that even if they had made their saves they were still smouldering crisps.