I modded my version of DF to send endless waves of elves clad in iron armor at my fort of 50 stout dwarven warriors.
We held them off for one year. After a siege of a total of 256 elves and their uncountably numerous mounts, about half of the army was crippled and the rest were scavenging the dead for armor. I couldn't get steel armor and weapon production going in time, and the elves were wielding mauls, which dwarves can't wield one-handed. As a result, most of my soldiers were wearing the crappy elven armor, and using only shields.
Another wave of what must have been over 500 invaders left me with only one healthy dwarf, and about 25 cripples and children scattered all over the place. My founding seven made a last stand in the dining room at the bottom of the fort against the elven high prince, 80 elven knights, and 50 war animals. Only my former high master armorer could now walk, and to him was passed the mantle of expedition leader. I ordered him to build a wall that sealed off a key corridor, trapping the elven war party in my dining room.
At that point, I received the notification of a child's death. I looked him up. It was the only son of the new expedition leader. His wife had already been killed by elves, and there was nothing he could do for the rest of his friends. I got angry, and desperate for vengeance, and then it came to me in a flash.
The brook was next to the main stairwell, a 4x4 shaft leading down into the fort. The expedition leader carved fortifications into the wall. Then, he dug a tunnel leading to the brook.
Even as he dug, another massive siege of elves arrived on the surface. They found my book keeper, slayer of an entire siege single-handed once upon a time, now crippled and dying of thirst, and began beating him slowly into a pulp with their mauls. I knew there wasn't much time, so I had my expedition leader put a fortification to his back to prevent anyone from interfering.
At last he breached the brook. The water quickly filled up his tunnel, then poured past his waterlogged body down the shaft, inundating the lower levels. There was no way out. The dwarves trapped in the hospital were the first to drown. Other wounded axedwarves who had fallen deeper down in the engraved halls of the fortress had been ignored by the elven high prince's host. These were swept through the fortifications sealing in the elven host, where they confronted the high prince's forces again and were forced to make their own futile last stand.
The frenzied panic of the elves as they realized death was coming and fled in every direction or searched for escape routes futilely in dead-end mine shafts was utterly beautiful. Some of them, the elven high prince included, struggled to swim against the flood, but it gradually forced them backwards until they were in a back room behind the meeting hall. It was there, just as a goblin ambush finished off the last of my survivors on the surface, that 130 members of the elven host drowned with their leader.