The High Priestess of the BBEG has this magic rock that spills black oil everywhere. This black oil corrupts and mutates anything it comes into contact with turning it into a tentacled monster bent on destruction.

Our party catches up to her just as shes about to pull off this monstrous ritual that would summon the source of the Oil. We start hammering our way through her minions when one of the mages drops an Otilukes Resilient Sphere on her just as she finishes the ritual. Oil explodes out of the Ebon stone coats the inside of the sphere and starts filling up. This, while saving us from the direct effects of the oil does not stop the summoning.

Shadowy tentacles start forming in the air around her and a giant alien face starts peering through a hole in reality. The stone is the source of the summoning and we can't get to it.

Here comes the epic bit. My paladin/former thief Allaine takes up his Holy Avenger and, using its Magic Resistance, plunges through the sphere into the sea of black oil and swings at the Ebon Stone. Its armour class -10 (1st ed btw) and I'm 10th level so I need about a 17 to hit or so.

Natural 20.

The stone shatters and the eldritch abomination begins to retreat. Allaine is horribly sick and dying, and has about 3 rounds before being mutated into a hideous monster. So I leap through the rift with the eldritch abomination scoring massive damage with my Holy Blade. The rift shuts and Allaine is lost forever in another dimension, doing battle with what later turned out to be Nyarlathotep's avatar. The party built a statue for him.

We played a campaign a few years later with a DM who was a player at the time of my epic sacrifice. We were doing a second generation kind of thing and when we went to visit Allaine's statue we notice the sword wasn't made of marble but real steel. And radiated magic. And could be taken down and wielded. And it talked. I got to roleplay my party members freakin sword. So much fun