The campaign that I ran, which lasted a little under a year, had a rather climactic ending, though not the one I expected. I sent two Assassins after the party, as they were resting up before the final encounter. Now, I should back up here. I supplied the party with EVERY friendly NPC that was still alive. They were all staying in a largish citadel known as Castle Coran (due to its centrality to the city of Con Coran). The two assassins sneak in, and have a FIELD DAY. I give the party some 20 opportunities to make listen checks, but they fail every one. So, when one of the party members is awakened by a knife sliding into her armpit, aimed at her heart, there are literally only five people left alive in the castle, including the four-person party. As she slid the knife in, the crazy elf Assassin sang Elvish lullabyes to the character (a Maenad named Psyche). She told Psyche to give up, that all of her friends and loved ones were dead, with the exception of the party and her brother (the Duke; they were saving him for last). The player told me later that she had nightmares about someone doing just that for weeks. I call that a DM-win.
Anyway, as this was happening, another of the party members (a Thri-Kreen named Tik'tak) was being attacked by another crazy elf; this one an Eldritch Knight. She was decimated by spellz. The Eldritch Knight, after crushing another of the party members (a Half-Giant named Raam), used every evocation spell available to her, yet still the Thri-Kreen would not fall. So, she did what every logical spellcaster does: she casts Enervation. A lot. It ended up killing the 17th-level character by means of negative levels. While this exchange was going on, Psyche had succeeded on her Fort save against Death Attack, but not against the Eldleaf Poison (basically, more-potent Drow Knockout Poison) that the Assassin had forgotten she had put on her knife. Out goes Psyche, and the Assassin (failing a Spot check BADLY) believes she's dead. She rushes out to one of the other rooms, and catches the Cleric (a Human named Landon) with his back turned. The very FLIMSY Cleric. Landon goes down to a Full Attack with Sneak Attack damage. Psyche wakes up, and blasts the Assassin into oblivion. The Eldritch Knight, seeing her sister die, gets mad, and uses Power Word Blind on Psyche. Unfortunately, that the only spell she had left above Level 3. So, eventually, it became a fencing match between the magically-deficient Eldritch Knight (who <3s Fireball) and the blinded, fire-resistant Psyche. It was so very special. In the end, though, the Eldritch Knight gets fed up, and hurls her spear right at Psyche, finishing her off, and pinning her corpse to the wall above the mantle. The players were satisfied, if a bit unhappy.