Ridley (Metroid)
Ridley's status within the ranks of the Space Pirates is unclear, with some sources stating that he is the leader of the entire Space Pirate race, whereas others portray him as simply the Pirates' military commander or even a mere enforcer within the Pirate military ranks, subservient to Mother Brain or Space Pirate High Command. Regardless, he is consistently depicted as a ruthless and cunning tactician who never passes up an opportunity to bring his considerable ferocity to bear on the battlefield, opting to overwhelm his opponents with an unwavering onslaught of attacks from his mouth, claws, and tail. He is also incredibly cruel, actively taking pleasure in the killing and torment of others; at one point in the official manga he taunts Samus by claiming he may have devoured her mother's corpse after killing her, and a Space Pirate log entry in "Metroid Prime" notes that being the mainstay of the Pirate security force is "a job he will certainly relish."
AM2R
The Metroids the player fights have four main evolutionary stages – Alpha, Gamma, Zeta, and Omega – which have been altered compared to their "Metroid II" counterparts, including new techniques used in battle; Alpha is the least altered, having only been given a new dodge move, while Omega has been altered the most, having been changed to earth-bound enemies that trap the player. The player confronts these Metroid bosses often and has to defeat 55 of them. Among the newly added bosses are non-Metroid enemies such as a moving statue.