Mechaniloid

Mechaniloids are robots that have below-average AI and a more mechanical shape than a humanoid shape (like the Robot Masters and Reploids). Mechaniloids also have the ability to go Maverick. Maverick Mechaniloids are the main enemies faced in the Mega Man X series and then every main series (Zero, ZX) since. They come in all sorts of forms including the Bat Bone, B Blader, Deerball and more. In the Zero series, there are different types of Mechaniloids that are slimmer and some that are more like X. Mechanaloids seem to be customizable to do just about anything, from construction to excavation. It is believed that the "standard procedure" is for a small army of assistant Mechaniloids, all specialized in a certain field, are typically sent with a single specialized Reploid for whatever job is needed at the time.

Mechaniloids are the main enemies in the stages of the games and have a wide variety of purposes such as attacking the player, serving as obstacles, some of whom can't be destroyed and serving as platforms or other helpful necessities. Many drop items that heal life, weapon energy or E crystals. Large Mechaniloids commonly serve as sub bosses in stages.

Trivia

 * A Mechaniloid is always the "intro stage" boss of every Mega Man game (with the exception of Mega Man X5) starting from X2; this trend even stays up to the ZX series.
 * It's speculated by fans that Reaverbots are enhanced Mechaniloids, but that was not confirmed by Capcom.
 * In rare occasions, Mechaniloids are shown being used by the protagonists, like in Mega Man X: Command Mission.