Originally I had thought of a creature something along the lines of a griffin but in the end I settled on something more like a sea creature like a ray, adapted to survive in the air.
Having not played Rift the original design of the environment contained a city and appeared more tropical but after a little research I altered the environment to appear more similar to that of the Plane of Air from screenshots I've seen. I figured that if the colossus was situated in the correct locale it might appear more natural to the game.