Oh god, easy one, the infamous-in-my-group "Massacre at the Funeral" in which my players basically destroyed the entire combined forces of
The Steading of the Hill Giant Chief in something like 10-15 combat rounds in late 2E (post C&T and S&M).
As time goes on I've forgotten exactly what happened but it's something like:
1) The players manage to lure and kill the Hill Giant Chief's son in such a way that it appears to be a horrible accident (this took a lot of work and a lot of spells from the Elf Wizard).
I'm not sure if they had a plan at this point, because the wizard's player, my brother, was extremely good at keeping his mouth shut about his plans, because he didn't want to tip me off.
2) The Thief, with his ring of invisibility and boots of elvenkind of (the quiet ones, whatever they're called) recons the Steading extensively, eventually only leaving because his player has become so freaked out by my detailed descriptions of giant-sized furniture and fittings.
During this time he discovers the giants are planning a pyre-based funeral the next day. The players go to the other end of the sitting room and confer. I become a little worried, but I figure they'll just use this to determine exactly the disposition of forces in there so they can plan guerrilla assaults or whatever, or more likely, to try and sneak in and nick stuff, or just wait until the giants are drunk and attack then.
3) I work out how the funeral is going to go down, full honours, almost all the guards (orcs, ogres, etc. IIRC) - and all the adult male hill giants (and most of the women and kids too), then tons of feasting and drinking, and maybe some raids on the humans in his honour afterwards.
The players have sent the Thief back in and got pretty much all the details, and the timing, but I was still in this delusion that they were just going to take mild advantage either sneaking in or waiting for drunken-ness.
I was
very wrong.
4) The Wizard very carefully selects his spells to memorize (he wouldn't let me to see them, which I guess was fair enough, he has never cheated at a game in his life), and the Human Thief and the Dwarf Fighter/Speciality Priest of Clangeddin go through all their spoils from countless adventures for consumables.
Was when I got a bit more worried. Again a lot of planning down the other end of the room.
5) The funeral commences, and I'm describing it in great detail - the PCs are basically whatever the maximum range of the spells involved were away (quite a long way, I want to say like 200 yards but I think it was less or maybe the wizard dimension door'd or something at one point), I can't remember where/how they were hiding, but it worked (possibly some sort of cave or artificial cave). Anyway, the orcs are formed up in ranks, a wild funeral oration is being given by the chest-beating, hair-tearing chief, the ogres are trying to shows some decorum, and so on.
6) Then the BUFFENING begins. So many potions were drunk including Giant Strength potions. The potion miscibility table got a lot of rolls that day, but they all were positive or neutral. So many low-mid-level buffing spells were cast. Enlarge, Stoneskin, Invisibility amongst them. Haste I think got cast later. There was other consumable stuff too. Basically they blew most of what they'd been failing to use for like 10+ levels. Scrolls were involved. The Dwarf somehow ended up 24' tall.
I was pretty much going "OH NO" at this point.
7) The wizard commenced bombardment, opening up with Fireballs (wiping out virtually all the orcs immediately) and as the giants and others started drawing weapons and running towards him, they found that they were surprised by two giant bastards, one of them coming out of invisibility and the CARNAGE oh god. The Dwarf is of course screaming about the "wrath of Clangeddin" and basically looks like the Avatar of Clangeddin at this point.
It was horrific. Giants were dropping left right and centre. Some started to flee but got cut down or nuked. Admittedly it was 90% the F/SP and the Wizard, but I think the Thief had Improved Invisibility from something which helped him.
Some of them took longer to die, but no-one actually managed to reach the Wizard, and I'm not sure they even managed to damage the other PCs much thanks to Stoneskin.
8) After quite a few rounds of this (I guess 10-15, but it might be more or less), all the giant-side combatants are dead, and only the women and children, who ran back into the steading and formed what defences they could, are alive. The giants agree to give them their treasure and stop raiding demihuman lands for a hundred years (or something like that) if the PCs will just go away.
I shorted them on the treasure, but they didn't seem to mind or notice. They'd already achieved a legendary and basically flawless victory which I had profoundly failed to see coming, so I can understand not caring. This is still brought up like every three-four sessions with those guys, 20+ years later.
