Ridley (Metroid)
One of Adam's final missions to Samus is to finish off Ridley, whom Adam fears might be more dangerous than the Metroids if left unchecked, and claims Samus is the only one capable of stopping him. However, Samus later discovers his corpse after he is killed, having had his energy drained by the Queen Metroid on the Bottle Ship. His mummified corpse turns up again in "Metroid Fusion" on the BSL station, after having apparently been removed from the Bottle Ship by the Galactic Federation and placed in a sub-zero storage room for further research (potentially into further bioweapon applications). It is later infected by an X Parasite, allowing it to gain the ability to transform into Ridley's likeness, known as . Samus later defeats the Ridley mimic and absorbs its Core-X, regaining her signature Screw Attack. What was left of the cloned Ridley's remains were destroyed along with the X when the BSL station crashed into SR388.
Big Bad
The main villains in Season 6 were the Trio - Warren Mears (portrayed by Adam Busch), Jonathan Levinson (portrayed by Danny Strong) and Andrew Wells (portrayed by Tom Lenk) - followed by Willow (known in this phase as Dark Willow), portrayed by Alyson Hannigan. Series creator Joss Whedon stated on the Season 6 DVD that the true Big Bad is life itself; and how, as time goes on, it becomes more and more people's worst enemy.