Even though KH3 is headed toward the sort of animation that has a more smooth, cgi look to it, I'm not really feeling any of the Pixar-type movies just yet. If it had to be a Pixar movie, I'd probably choose Toy Story, since it'd be neat to be shrunken down among the toys. I know the shrunken-down thing has already been used in BBS in the Cinderella world, but Toy Story especially holds a special childhood nostalgia for me. Another movie I'd be interested in seeing in KH3 has to be Atlantis. While the movie itself may not be a favorite, I thought some neat gameplay elements could be incorporated. Since there was already talk of "riding" things in recent interviews about KH3, I thought it'd be fitting to have a vehicle-based battle, taking advantage of the Atlantian vehicles that are already in existence. Besides that, the location would provide for visually stunning maps and scenes.
