Okay, my results.
I started a new fort with the sole purpose of breaching the house of Fun.
I dug a RIDICULOUSLY massive cistern two levels above the top room, and stationed one of my miners (as a recruit) at the bottom of the staircase leading down from it. I channeled out a 2x2 area once the cistern filled (losing three dwarves to the underground river's locals. I swear, they all JUMPED in) and Operation: Down the Drain was officially started.
Sequence of events:
Miner climbed up into cistern. Ringmaster revealed himself and killed another miner. My first miner went into a RAAAAAAAAAGE!!! and killed the ringleader by herself (spoilered for violent assumptions)
probably by carving a new face in its chest. With her pick. To replace the old one. That she had smeared all over the walls.
Tentaclowns revealed themselves, killed the miner, another miner, and half my kittens. Tentaclowns drowned, Path to HFS walled off, hermit fort begun.
End results:
# Clowns dead on unit list: 26 (ringmaster included)
Out of: 31.
Visible Corpses: 6
Humanoids dead: All
Out of: 147
Conclusions:
Draintrap more useful as a drowning trap. Few if any clowns were flushed.
Tantrumming legendary miners FTW
Solution ineffective against frogclowns and !!clowns!!:
Frogclowns: Can swim. Solution: Add more (like, metric ****loads more) water, flush them all.
!!clowns!!: Boil the water away before it reaches them, same solution as frogclowns (drain an aquifer if needed, infinite + comes in as high a quantity as you like!
EDIT: I sacrificed a half dozen dwarves FOR SCIENCE!
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