This was actually the last adventure I ran for my all-elven FR campaign. I have a slight problem with my group as at least one of the guys is way more intelligent than me (he has a PhD in Microbiology while I have a degree in Contemporary Dance)...
This player has 2 characters: a druid (known as "The Druid" *wave fingers mysteriously*), who spends most of his time wild shaped into strange things like albatrosses, and a wizard with a flying construct familiar and a penchant for the gaseous form spell.
The Druid spotted the Kadtanach rampaging across the Realms and basically tracked the thing from up near the clouds, then chose to investigate more closely, scouting the howdah structures as a seagull. He very nearly got petrified by the basilisk so hightailed it out of the area and brought in the rest of the party as reinforcements. The mage sent her familiar up to deal with the basilisk (by having it cast invisibility on the creature, so its gaze attack wouldn't work!), then sent the group's toughest fighters down the beast's throat, under gaseous form and water breathing spells. Promptly inhaled by the beastie, the two warriors end up in the creature's lungs. As gaseous creatures cannot pass through liquids, they would stop at the alvioli, according to my biologist buddy. They then return to solid state, attach themselves via grappling hooks to the internal walls of the kadtanach's lungs, and start hacking away from the inside, in order to drown the creature in its own blood.
There was no way I could allow half a dozen 7th-level characters to kill off a CR 18 beastie with a couple of 3rd-level spells, so I was completely flummoxed. Eventually, I decided that, as the thing has Regeneration and Damage Reduction 15/magic, the damage to its lungs would heal very quickly ... and that the (nonmagical) grappling hooks would not stay affixed, so, after the first round (wherein the two warriors did an excess of 100 damage between them), the creature started coughing up blood -- and them with it, expelling them about 80 ft up in the air, at high speed...
The two fighters were very nearly killed by the experience but the violent bucking and swaying of the near-asphyxiated kadtanach pretty much obliterated the gnoll ranks above, as well as destroying the ballista and three of the catapults. (When the party eventually flew up to land on the thing's back, they were amused to find the last of catapults, the Animated Object, clinging on to the howdah for dear life...)
Meanwhile, H'Jyord had passed the helm of control to Sylkess and teleported into the ranks of the remaining party far below. Their battle was grueling but, eventually, just before the evil archon was about to retreat, he was killed by an astonishingly brutal longspear crit.
And, as for Sylkess, she was promptly knocked unconscious in the Command Tower, as her beastie threw itself about in near death-throes.
The group have now gained access to the howdah and are exploring the various towers, pretty much with impunity. For the last couple of hours, the kadtanach has shown increasing independence, as its master lolls about in her chair, stunned senseless. I closed the session with the huge creature suddenly calming down and starting to look about for targets on the ground to stomp on. They haven't found Sylkess yet, and she's just woken up.
So, while I couldn't allow the group to kill the kadtanach with a couple of gaseous form spells, a single water breathing and some grappling hooks, I did think the idea was spectacular and worthy of some serious merit -- so I effectively had that combo kill off most of the gnolls instead, while the colossal beast Regenerated away all the internal damage it had been dealt.
Was I fair or perhaps too lenient? Would any of you have judged this differently?
Keep in mind that according the module, the helm was crafted for use with that particular animal only. You could say that it only works on Kadtanachs (which will be very rarely - if at all - encountered again), or that it works on just that one particular Kadtanach. So it's practically useless, as my party found out when casting Identify on it.
