A titchy bit of background here. I'm running a HERO System game for some friends, in which everyone plays video game characters. They're shifting between video game worlds, fighting against a force that seeks to corrupt the worlds and destroy them. So, pretty standard fare.
And last session, I sent them to a Dwarf Fortress world.
They appeared deep in a tunnel and were quickly found by the Captain of the Guard. One of the party members went invisible and followed behind as the rest were led to the throne room, where the King of the Mountainhome interrogated them for a bit and eventually informed them that a vast goblin/orc horde, led by a mighty Demon, was on its way to the Mountainhome... and that the Humans and Elves had already been eradicated entirely, that the Mountainhome was the final stronghold.
The players agreed to help in the defense, and they were taken to the treasure chamber and given dwarven Artifacts to help them fight. The stealther, who had impressed the King by popping into plain view in the middle of the throne room, was given an artifact longsword with a bit of history behind it. Nazushrakus, Bloodthirst, forged by a dwarf whose melancholy at the news of the final destruction of the human race triggered a fey mood. He came out of the forge, cast himself into a river, and left Nazushrakus embedded hilt-deep in a solid granite worktable.
And so they led the defense on the main front. The party sniper took to the walls and commanded the wall crossbowdwarves, a character with mechanical knowledge was tasked to maintain the traps and command the ballista crews, the super-strong melee fighter stayed on top of the walls to command the catapults and to throw the rocks from their ammo supplies, and the stealther was given command of a troop of ambushers and sent into the field.
The first waves, mere goblins, died easily and without trouble. The subsequent waves included many orcs, as well, but the defenders managed to hold them off, though the other walls began to fail under the onslaught. Then, as the battle reached its peak, the immense form of the great demon Engnun Lozuolsmo came into view, a captured dwarven artifact over his shoulder-the great adamantine axe Dorengast, Diamondcleave! The captain of the dwarven guard and the four champions that remained charged out onto the road as dwarven faces on the walls poured magma onto the battlefield; the ambushers fled into the tunnels, as the stealther snuck onto the road behind the Demon. The battle was surrounded by scorching magma, but the party battered the demon until it began to fall over unconscious... at which point the otherworldly corruption that they had come here to right consumed its body utterly, infusing it with impossible strength. With one swipe of the great Dorengast, Engnun slew the fortress's four champions, along with the heroic Captain of the Guard.
The strong one kept pelting Engnun with the heavy catapult stones, though the arrows of the tower guard failed to penetrate his hide. With a heave of his great arm, Engnun cast the greataxe Dorengast at the sniper, who avoided it by diving off the wall, stopping just short of the magma pool before scrambling to safety. The party valiantly struggled, until the assassin leaped from cover and sunk Nazushrakus into the demon's side, then leaped. The shade of Litast Tangathlor, the smith who forged the longsword, appeared beside the assassin to guide his strike deep into the heart of the corrupted Demon, and it roared, slumping to the ground as the flesh melted from its very bones, leaving behind nothing but a writhing mass of raw corruption and a pile of blackened bones.
As the party prepared to leave, the King thanked them from the depths of his heart as they returned the artifacts they had been loaned. He opened the forges to them, and the master smiths worked tirelessly to make what improvements could be made on their equipment.
But for the assassin, who had so impressed the King and who had sated the bloodlust of the vengeful spirit of Litast Tangathlor, there was another, far greater gift. Though dwarven law prohibited the passing of dwarven Artifacts into the hands of other races, as they were an irreplaceable part of dwarven history... Nasushrakus still had a story to be written. The king bowed low as he placed the sheathed blade back into the assassin's hands, thanking him and the other outsiders for their heroism. The marks of battle even marred the throne room; the other walls had fallen before the horde, and it was only the passing of the Demon and the loss of the dark strength they drew from the Corruption that tainted him that broke the siege and sent the enemy fleeing.
The mountainhome Sarveshkizest was safe, for now, and the travellers bid their newfound friends farewell as they moved on to the next realm in need.
{This was a tabletop roleplaying session I ran recently for some friends. It went well.}