The Hydra was my pet feature, a monster I wanted in from the start. We designed whole areas of the game around it. I personally spent about six months on and off getting all the movement algorithms and physics for it in a working state. Everyone was pretty skeptical it was even possible when I started, so I kept it pretty low profile, but once I got some early rough AI drafts up and running, pepole would sneak one into a map, check it out, get all excited, and start pushing me to hurry up...