Mavericks replace the Robot Masters, and Sigma replaces Dr. Wily. The stage boss Mavericks are based on various types of organisms (usually animals, but plants and fungi are also represented) instead of being humanoid, as were most of the bosses in the classic series, although their attacks and names are usually based on mechanical or chemical phenomena or laws of physics like in the original games. The main group of antagonists in each game, which are fought as mid-bosses and/or fortress bosses, are normally humanoid in appearance.