It's a legendary Pokemon that lives in an alternate dimension--err, well, it lives in this place called the "Distortion World" or something, and it has the ability to travel between there and our world. The Distortion World it lives in doesn't seem to be fond of physics though, since you can walk on walls and stuff while you're there. [It was both cool and creepy there, and he's not entirely sure if he ever actually wants to see that place again.

Let's see, what else did we have written down here--] Giratina is a ghost and dragon-type Pokemon, and some legends even mention it with Dialga and Palkia as being part of a trio that helped create Sinnoh and the world and stuff. But then it supposedly got banished to the Distortion World for being too violent in comparison to the other two.