Then ithought maybe you could attract certain monsters- minotaurs, medasue- by equipping a zone appropriately. While not friendly, they might be content to sit in the labyrinth or necromancers tower rather than invade. I was thinking it could be zone based. Build a horde in a tall tower, when a dragon comes, it might move in. While such creatures wouldn't necessarily halt a siege, they are alive and MIT do helpful things. Or eat a dwarven caravan.
This sounds neat. Aside from applying a spell which attracts the critters magically, though, you'd need to be attracting a sapient creature who hears of it. Attracting hydras or rocs or something would be pretty hard.
This also gave me another idea: Wandering adventurers and mercenaries. Say you're in an evil biome. One day, a group of crusaders stops by your fort and offers their services for a year in exchange of a place to stay. You can't control them, but they're all really good military dwarves and they'd be off after a year, or if you actively decide to kill them or something. If you decide to turn them away, then they'd just pack up and go. Some mercenaries and adventurers wouldn't be so nice though; if you don't let them stay, they'd attack you.
They should walk around the fort punching people and kicking pets, causing unhappy thoughts.
Maybe, but I think most of my adventurers would rather screw with delicate stuff (i.e, deconstruct random buildings, especially mechanical stuff, pressure plates, etc) or just kill everything if they were angry, rather than randomly attack people nonlethally. This is, of course, ignoring the possibility of "roughing up" a fortress with the implicit promise of more if they don't obey soon...
Personalities could come into play. I'd like the idea of a Titan entering your fort, making demands, and getting so pleased with them being met that they start to really appreciate their fort, and the fort appreciates the titan for killing goblins until eventually you get the titan lying down in the middle of your grand hall while dwarven children play on his rumbling belly! Or you just might end up having a tyrannical titan who never seems to be pleased...
Those sound like lots of fun! It would also help when goblins came. Imagine having an old, decrepit dragon watching the dwarflings, until it heard that an enemy would harm the children...or, less Fun, a moronic officer of your own fort. (Cookie for the reference, because why not?)