So, I had an FB (giant humanoid made of ash, no special powers) come in through the third cavern layer, where I was trying to set up a minecart based magma mover, filling a big cistern at z -20. To get magma in the carts, I had a dwarven water reactor built, following
this design exactly, but I hadn't yet sent a bucket brigade to fill it from the water in cavern 2, so it was empty, but with pump, two water wheels, and a hatch over the pump input with attached lever, and the ramps removed from beneath the water wheels but not the pump input.
Ash monster shows up, I send in the militia, my mace dwarf, who as it turns out doesn't have a mace yet shows up, knocks a hand off with his shield before being promptly punted into the magma pool by the FB (discovering candy in the process, so I guess yay, praise the miners?). Next on the scene is a spear dwarf, a brand new recruit with neither spear nor meaningful armor. Skull caved in immediately.
Then I go try to get my military sorted out so someone with an actual weapon will come deal with this crap, and when I glance back, the FB is dead! I check the reports, and the most recent one has him getting clobbered by a pile of flying logs, which are scattered in the reactor trench along with the FB parts. The pump and water wheels are deconstructed.
I assume he broke the pump, and the falling water wheel parts got him, but don't they just fall, or do they explode? I don't know where he was standing when he broke the pump, but I would assume it would be in the accessible tile of the pump or on one of the adjacent diagonals SW and SE of the pump.
He was made of ash and so was somewhat inherently delicate, but still, as my carpenters discovered after I played around with minecart supplied drop chutes for wood, falling logs are not harmless. I would like to mount a large number of water wheels suspended over a single supporting machine component as a trap for building destroyers. I've got some Bloodthorn in the caverns for heavy logs, does anyone know if falling height affects the lethality of falling items? I could put it in a tall chamber with a vertical axle holding the wheels high above the hapless building destroyer. Gold mechanisms are another potential item to drop (I assume they deconstruct when unsupported, like water wheels?). If you build it in a fortress entrance anteroom, you could get a troll to drop it on his whole squad.
I know there are better building destroyer traps, like supports to generate cave ins, or doors holding back water and/or magma, but I think this one's entertaining, and what it lacks in lethality, it makes up for in ease of cleanup and lack of cave ins. Has anyone tried something like this?
EDIT: fixed broken link. The iPad's copy/paste and selection system takes a dwarven approach to doing what you want when you want it.