Ahhh, the Mecha Dragon. Always such a curious fable in the gaming industry. The beast itself was a background layer, and since that section is an auto-scrolling part of the game, I can tell this was no easy feat. And since it's a pitch-black room, I could tell that they simply used Yellow Devil, another boss, And cut the LEFT side of the section off and use that as a hit box, then made the blocks the objects for Rockman to stand on. They were also able to get it to have a "bobbing" motion as if it's flying across the room. Neat!