I once set Spoiler Monster number to 500 and then built The Hammer to destroy them.
At the top of the map (Z=230, mountains) was a hole that extended all the way down to the Candy tube. On top of this was the Hammer, which was a 20 z-level high, 30x30 excavated granite mass.
This fit into the Anvil, which was built atop the tube right under the caverns - the Anvil was a 3 layer area full of bait animals and cheap bait furnature and doors to try to mass the Spoiler Monsters in there. Everything was constructed, floors, walls, everything so as to not leave any survivable voids when it collapsed. There was a smaller cave-in plug to prevent the Spoiler Monsters from entering the main mineworks. This was at Z=10.
The shaft downwards was exactly 30x30 below Z=220.
At Z=30-37 there was a 70x70xZ=7 cistern with a constructed floor full of water. At Z=220-227 there was one of magma to encase any possible survivors in obsidian.
500 Spoiler Monsters spawned, and (slowly, at 1 frame per 2 seconds) massed inside the Anvil.
When a significant number of them, probably 470 or 480 (the unit list was FUN) I had a dwarf pull the lever to drop the "hammer". It was supported by a constructed wall extending out below it with a support rigged to collapse built atop the wall and the hammer atop that.
The hammer dropped. Literally. 3 minutes later (framerate? what's that?) it landed.
Spoiler Monster paste. It took almost an hour for my framerate to improve due to the liquids from the cisterns sealing the Hammer.
It was epic. One dwarf died in the making of this moment of epic, because he was stupid and standing on top of the Anvil idle.