Yesterday (and the day before yesterday) I met up with some friends to play in our mini BX campaign using module B2 The Keep On The Borderlands. We don't get to play often, like once every few months, and I'm running this game for a year and a half now. It's very satisfying to see people who never ever played rpgs going all mad about D&D, and I think I did everything to provide them with the best old school fantasy experience possible: loads of monsters, unreliable NPCs, and a good dose of Dungeon Master's sadism. (Laughing at their 1's and exulting at monsters' 20's do more than half the trick, you know.) During the session we played on the 25th they killed the Owlbear, fucked around with some Grey Oozes, and finally entered the Temple of Chaos. They were very clever (and lucky) in pointing directly to the chamber with the acolytes, Sleep-ing every one of them but one, who they Charm-ed to get information on the lair of the Evil High Priest (they called The Greater Evil). By the time the session ended they had a good plan, a good amount of information, and I was pretty sure that the next game would have marked the end of this mini-campaign with a great final climax.
But then, you know, players always have to surprise you and so they did.
Instead of heading directly to the Temple, they stopped in room 56 to fuck around with the evil cultists. Once again, they very cleverly made use of the Sleep spell, and had every four of them in one round, with the advantage of surprise. If you know something about B2, you know how important is to be sneaky at this point of the game. So, instead of moving on to the final confrontation, they eventually decided they'd slay three of the cultists, save one for some interrogation. (The kind that involves cutters, pliers and hot iron.) Needles to say, the cultist woke up screaming like a pig. I rolled for wandering monsters once, twice, three times and finally someone in the temple heard the noise and ring the massive bell. Loads of undead was approaching the room from north and south. If you ask me, that's a situation in which you run as hell, making room among the undead by turning them to reach the exit as fast as your short halfling legs allow you. If you ask my players, they're more like "WHOA TONS OF MONSTERS! COME AND GET IT YOU WANDERING PILES OF XPs!", and thus they entrenched in the room, cast Hold Portal on the northern door and decided to fight till death. With AC 2 Dwarves in the front line, polearms in the second, and AC5/3hp skeletons approaching two at a time from the southern door they were doing pretty good, until some cultist started to launch molotov cocktails inside the room to set everything on fire (save vs. poison or suffer 1d6 damage from carbon monoxide EVERY round). So out they went to retire, and some other cultist cast Darkness on them. And you know, skeletons don't need no light to beat the shit out of your stinking adventurer's ass. They eventually lost one fellow in the darkness (his fate unknown, as of now), and managed to flee.
Note: The only Lawful character in the party, a Cleric (also, the one who suggested they'd torture the cultist fucking up every effort of sneaking inside the Temple), decided not to destroy the evil scripts found in room 56. Instead, he would keep them for study. Ironically enough, destroying them would have granted him no less than 600 XPs, not to divide with anyone else. His comment after the game was: "I promise not to torture evil cultists for the sake of it ever again. Nor to collect satanic memorabilia instead of setting them on fire, for fuck's sake!"
So, wounded and sad they returned to the Keep. They told the lord about their last foray into the Caves of Chaos, and he was all "You fools! You unleashed the doom above us!" and "Let the women and children go! Fortify the Keep! THEY'RE COMING FOR OUR SOULS!" and around midnight of the same day, the Army of Darkness was slowly crawling out of the woods to raze the Keep.
So yes, the next session is most likely going to be some kind of small scale war, in which the party will finally confront with the undead servants of Chaos. (And possibly die in the attempt.) What a brilliant mess they made! Nonetheless, every last one of them was so amazed, so happy about it, and a little sad this game is about to end. It was fun as hell to play it, and doubtless the best campaign I've ever ran.