I'm running a Pathfinder-modified version of the Dungeon #90 adventure Elfwhisper (3.0, I believe), and the final boss encounter is set up to be a TPK against my party. I'd like to avoid that.
The party consists of a lvl.7 diviner with virtually no offensive spells (for house rule legacy reasons), a lvl.7 bow ranger, a lvl.6 antipaladin (who I'm allowing to smite evil for story reasons, with the use of hero points and some good RP), a lvl.6 shadow sorceror (with a shadow raven familiar), and a lvl.6 NPC cleric (their rogue is currently missing). They don't have a great deal of magical or alchemical equipment - only the ranger and antipaladin have low-grade magic weapons. They do have the aid of a dying lvl.4 NPC bard, who was attacked by the boss, and the antipaladin is being protected by elven spirits as though he were under a stacking mage armor effect. The party has proceeded to attack the boss over a harp of charming it has.
The boss is an advanced half-fiend shambling mound with some odd powers. It has fire resistance 30 and cold and acid resistance 20, a fairly high AC and attack as well as hps, and the thing that concerns me most: its spell-like abilities, which it uses as a 14th level sorceror. The one that concerns me most is blasphemy. That one, cast at such a high CL, could be a TPK on its own. If you have the magazine, you can see the others, but they don't concern me as much (except maybe for unholy aura, which would grant it SR 25 vs good spells/spells cast by good creatures once cast!). Honestly, the spells appear to be chosen out of a hat full of "let's destroy the party." On top of that, the boss is supposed to be able to use the harp of charming, which might conceivably take out the party's main firepower/muscle if they fail their saves. Its main concern is to kill the sorceror, who is an elf. She has currently gotten too close, and is grappled. Did I mention that it has a reach of 20'?
I don't want to nerf the encounter entirely, as it should be hard, but obviously I don't want to slaughter the party. On top of that, they've been grumbling about not succeeding at their other quests, so they probably will be unhappy even if they survive this unless they defeat the boss somehow. Since the game is supposed to be fun for them, and we've been playing a long time (pbem) without what they consider significant victories, I want to make it possible for them to defeat the boss - but I don't want to make the boss a pushover, either. I hinted earlier in the game that the boss could be controlled by the harp it now has, but a) they don't seem to think they can get the harp without killing the boss, though the familiar is holding it along with the boss, and b) they don't seem to have realized that the boss IS the boss I hinted about.
Since they aren't carrying much in the way of offensive power that can defeat the mound, especially with its fire resistance (which might as well be immunity when it's that high), their choices are to simply run away and come back better equipped, which they don't want to do because they're in the middle of tracking down the missing rogue, or abandon the harp entirely, which they don't want to do because they think it's important to the plot. OR... we're looking at TPK material. Or I DM fiat that they win somehow, which is a pretty hollow victory.
- the boss can speak so long as it's within a 40'r of a dead tree (unhallow tongues effect), in the center of a clearing in some ruins, which is its lair. It doesn't want to go too far from the tree due to the SA spells centered on it, but can be lured away because it's not too bright (though it doesn't speak like a caveman or anything). It has dropped some plot hints about the antipaladin, and wasn't inclined to attack him (or anyone but the bard (a half-elf) and the elf PC) at first, but now he has attacked it and the gloves are off.
- the boss has, in the story, been killing off elves in the region for a long time. Not just once long ago, but continuously since it arrived; it just arrived so long ago that, combined with general hostility towards elves in the area, most of the killing was long ago, and no one worries about a missing elf here or there now. The harp is instrumental to keeping it under control, and the boss knows that the harp can do that. The boss is actually the pawn of a greater power, the true villain of the campaign, which the party doesn't know about yet (though the missing rogue does).
- there is an escape hatch nearby (within the clearing): a fairy ring that leads to the outer part of the forest. I've described a desecrate effect on the dead tree as the Weave unravelling into wild magic just around it, again for story reasons. (The diviner can see this.)
- I do allow hero points to be used to get hints on how to deal with situations.
So... is there a way to save this situation without being extremely heavy-handed with hints and cheating in favor of the PCs? They do have plenty of hero points (due to an old house rule that removed the limitation of max.3), so they can avoid insta-death, but... well, they haven't come up with anything clever and neither have I. Best-case scenario at the moment is that the boss crushes the elf, then drops her and leaves her for dead (though with judicious use of hero points she wouldn't be) and... I don't know, goes away for some reason. Maybe they even sever the branch holding the harp before it can use it (the ranger severed the vine it used to grab the harp before, but no one got to it before the boss picked the harp up again - not sure why she thinks it won't work again), and grab the harp. But I doubt they'd let it go (or use the harp to control it, since they don't seem to have understood that this is the boss the harp was meant to control, and with the bard dying and no one inclined to help him, no one can play it anyway), and if they did, they'd be unhappy about another "defeat." Quandary!
TL;DR: The boss is too tough for the party (with their limited resources) to win at the moment, but I don't want to nerf it too much. I would prefer that they have some sort of victory, even if they don't manage to destroy the boss. Ideas on how to achieve this? I'm no good at building monsters, which is why I used a published one in the first place. I suspect a story solution is called for, I just can't see the forest for the shambling mound. :P