I came and signed up just to share this, since it was so... unique.
I was sitting back and watching my fortress start to build above ground, most of it had been below before now. Suddenly, I got a message. A titan had appeared! No problem, I have a military force ready, I'll just... wait a second... it's surrounded by fire...
It was charging at my fortress, leaving a wake of fire, burning through the grass above ground. Now not only did I have to deal with a titan, but I had to deal with him in the middle of a raging fire.
Then, I saw that he was heading straight for a murky pool. He didn't bother going around like I thought he would, instead, he jumped in, intending to swim across. However... the pool started steaming up, and a few seconds later, the titan was trapped in a pit where the water used to be. His heat was his own downfall.
I ordered my dwarves below ground and locked them in and waited for the fire to go away. Luckily, it didn't go over the brook, so not everything was burnt. Also, I was building above ground with stone, not wood.
So, now I have a fire titan trapped in a pit... now what? Just keep him there? Build up my forces and then unleash him? Pour water on him?
Also, screen shot. Notice that there's the brook flowing right next to him.
http://img194.imageshack.us/img194/9333/firean.png