Ridley (Metroid)
Often considered one of the most memorable Nintendo villains, Ridley has been a mainstay of the series, having appeared (through various incarnations) in almost every "Metroid" game to date (all but "", "Metroid Prime Hunters" and ""). He has also appeared in the "Super Smash Bros." series, however, he had not been made a playable character until "Super Smash Bros. Ultimate" in 2018, making it also the first game overall to have Ridley as a playable character.
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.