@billd91, you're correct in identifying the adventure.
I could tell they were getting frustrated. It seems like every other session there is an unwinnable mission in this adventure. Luckily, they had a chance random encounter of an NPC follower with 160 HP, immunity to normal weapon damage, two attacks per round dealing an average of 16 points per hit. Without him, they'd have TPK'ed several times. But it's completely anti-climactic and takes the spotlight off the 4th level party. (Another reason why this adventure is really, really badly written - despite many claiming it to be one of the "cream of the crop" adventures for 5e.)
Except that the solution is something that can only be cast by a single (not exceptionally common) character class and also a higher level spell than what the adventure is written for.the solution is kind of out there in the open for them to see.
Right. And if that happened a few times, that would be fine. But nearly 1/3 (or more) of the quests are incompletable at the suggested party level - either they don't have access to specific spells, magic items, etc. And when they don't get treasure (or XP) from the quests they don't finish, it's just like running into a brick wall.Then leave it up to them whether they want to push on with a useless fight or retreat and see if they can find some magic weapon (or silver or whatever) that someone is willing to trade or sell.
They spent about half the session trying to deal with one of the unstoppable things the Cave of the Berserkers where the barbarians can't go lower than 1 HP unless you cast dispel magic (which you get at 5th level) or stone shape (which you get at 7th level) on the brazier - and they're 4th level, as suggested by the adventure. They came up with reasonable ideas to try, fought a desperate and unwinnable battle.Out of curiosity, did these things actually stymie your players or are you worried they might? If you're worried, I've found that players can be both far cleverer (and stupider, sillier, and more bizarre) than I expect. You know your players better than I could, but is it possible you're underestimating them?
I could tell they were getting frustrated. It seems like every other session there is an unwinnable mission in this adventure. Luckily, they had a chance random encounter of an NPC follower with 160 HP, immunity to normal weapon damage, two attacks per round dealing an average of 16 points per hit. Without him, they'd have TPK'ed several times. But it's completely anti-climactic and takes the spotlight off the 4th level party. (Another reason why this adventure is really, really badly written - despite many claiming it to be one of the "cream of the crop" adventures for 5e.)