My first real fun was with my first actually successful fort, in late .40d or maybe early DF2012: a bustling metropolis of two hundred dwarves with my first functioning metal industry (although with only copper on the map!) All was going well; the militia was training, booze was plentiful, everything was peaceful. Until a bronze colossus arrived.
I had heard about them, of course, and knew that this was no foe to be trifled with. I ordered the gates shut, manned the stockade and watched as the colossus approached over the endless dry plains surrounding my fortress. My battle plan was to soften the big guy with prolonged crossbow fire before engaging with my various weapon lords; I had plenty of bolts and the forges were now making them non-stop. Everything was set for an epic showdown.
The colossus helped my plan by simply strolling back and forth along the long stockade, allowing crossbow squads to leave and fill their quivers before returning to their positions. They kept peppering it for several weeks of game time; the bolts were used as soon as they could be made but I was in no hurry. Although the bolts were only copper, wood and bone they seemed to slowly have an effect: the colossus went prone and gradually its every part turned red in the wound tab. "Red means 'crippled'; that's good enough", I thought and opened the gates to let my two squads of weapon lords charge out, clad in copper armor and armed with copper weapons.
Yes, in hindsight I probably should thought that out a bit better.
To my horror the militia's weapons had no effect on the colossus, no matter how hard they hit. On top of that, even when the colossus was reduced into what I imagined was just a great bronze torso rolling around the plains, it could still push like a freight train. I watched as one by one my heroes flew from the melee and crashed several squares away into the ground, dead or unconscious. "I can still salvage this", I thought and recruited two new squads to draw the colossus away from the still surviving elites so they could be rescued.
As it turns out, dwarven military tactics aren't that sophisticated. Instead of new recruits drawing the colossus away, they charged the enemy outright and soon suffered the same fate as the veterans. I panicked and recruited most of the fort's adult population into militia and out they went, brandishing whatever weapons were left in the stockpile, including training spears and kitchen knives. As could be guessed, they didn't fare any better. There were now dozens of brave volunteers lying mangled and barely alive in front of my gates, and no one could be rescued while the colossus was loitering nearby.
Then the human caravan arrived. Two caravan guards joined the dance and by a stroke of incredible luck they led the colossus away from the gate, allowing me to start planning for a rescue and recovery operation. Unfortunately, as I had concentrated on what happened on the surface I was completely unaware of what was brewing underground.
As the death toll grew large enough, the dwarves remaining in their regular jobs coped with loss as dwarves do: the whole fortress erupted in madness and violence. I remember one blacksmith in particular: he was one of the first to go berserk and to rampage through the fortress. He first punched his dog to death and strangled a baby, then for some unknown reason he headed all the way to the surface to find more victims.
The victims in question were of course the injured heroes of the colossus battle. The berserk blacksmith went methodically from one injured to another, strangling and beating each of them to death. I remember actually shouting at the screen "NO NO NO NOT THEM FUCK YOU" or some words to that effect; then I abandoned the fortress so I wouldn't have to witness any more of that travesty.