dragon 1 -
had no front legs. constantly passed out till a caravan left my depo and passed by it, and the guards beat it to death while it was unconcious.
dragon 2 - went down a random single tile staircase in the furthest corner of the map to get access to my underground mapwide water mechanisms. smashed a floodgate, got stuck and drowned.
dragon 3 - came into my inner courtyard then crawled into my moat so it could break all the doors there. got stuck there for 3 years or so and could not get out, even when i took away some walls and drained the moat. so i got bored and shot him full of crossbow bolts.
dragon 4 - took a single bone bolt to the head from a legendary hunter and fell instantly dead a few microseconds after he appeared. the hunter actually hauled his corpse back to the butchers, which was a bit of a silver lining. many dragon tallow biscuits were had.
ive also gotten a titan, who was caught in a cage trap. i threw him into a pit with around 100 tame animals, thinking he would get rid of them all. after a few months of running around mashing kittens and getting lots of grey injuries he passed out from exhaustion and got kicked to death by a horse. repeated savescums showed this was not a fluke. nothing can beat a large pit full of 100+ kittens, puppies and horse foals. including goblin sieges with legendary weaponsmasters, berserk craftsdwarves and tentacle demons. im assuming bronze colossus who do not get tired, and anything that breathes/throws fire would be the exceptions to this. although firebreathers would doubtlessly die in the inferno they would create.