ok, this is the most evil, sick, twisted, and slow way to end your fortress. it takes time, and only works with 40, 80, 160, ect. dwarves
Dig down to an unused zlevel to start construction on a series of rooms. these rooms will be built connecting in pairs to another row of rooms, so if you start with 40 rooms, the next set of rooms will have 20 rooms, and so on untill you have but one room.
now to build the deathtraps. for this example, we will use 4 starting rooms, a,b,c and d, 2 secondary rooms (e, f) and one final room,
the rooms should be set up so that a/b and c/d share a wall. hollow out that wall and put in glass windows/blocks. then, in each room, put a pressure plate. each pressure plate will then connect to two floodgates, one in the room it is in, one in the room it shares a wall with. so, a pressure plate in "a" will trigger a floodgate in "a" and a floodgate in "b". the pressure plate in "b" will connect to a floodgate in "b" and a floodgate in "a". c and d will be set up the same way. the trick here is which floodgate opens. there will be 2 floodgates in each room: 1 leading to the secondary room (a/b will go to e, c/d to f) and one holding back water. if a dwarf pushes the plate in their room, they will get to advance to the next room, BUT they also have to watch their neighbor drown!
after the first round, there will be a dwarf dead for a dwarf in eahc second spot. so, Dwarf "a" died but dwarf "b" is in room "e". dwarf "d" is dead while dwarf "c" is in room "f". thee two rooms (e and f) also share a window. some idea: a plate in each room, hitting a plate will cause one dwarf to die and another to advance. this time make it interesting by making the trap different. have it drop a bear into the other room, or something like that.
finally you have one dwarf left, in one final room(with all your artifacts, weapons, ect) you can let him go, or have him pull a lever that caves in the room on him.
If you can't get your dwaves to activate the pressure plates, add a kitten with each dwarf.
you might wanna figure out how to turn off tantruming or melancholy.