Legionization is the process of removing part(s) of a Mobian's organic body and replacing them with cybernetic implants. It was derived from Dr. Robotnik's early experiments with creating cyborg warriors, which led to the creation of Monkey Khan. The process, in the case of unwilling recipients, is accompanied by brainwashing, rendering victims emotionless and obedient. Mobians who undergo legionization become members of one of the Dark Egg Legion chapters around Mobius.
The process was first utilized by the Eggman Empire some point after the Xorda's attack on Mobius as an alternative means of enslavement, since the Bem made it impossible for Dr. Eggman to roboticize Mobians. However, it differs from Roboticization in that it is often willingly undergone by various individuals who have pledged loyalty to Eggman. Even in these cases, however, a certain amount of loyalty has been ensured by the installation of explosives in the cybernetic implants of the Legionnaires that Eggman can activate at any time by remote or voice command. According to the Iron Queen, these explosives are implanted in such a way as to make them incredibly difficult-if not impossible-to remove. The term "legionization" was adopted after the remnants of the Dark Legion joined the Eggman Empire, as did the use of robes and the term "Grandmaster" for Sub-Bosses.
While its intention is overall sinister, Legionization may have some benefits, as evidenced by members of the Great Desert Dark Egg Legion. In particular, Beauregard Rabbot claimed that the process had repaired his "bum knee", and Matilda the Armadillo was equipped with arms that gave her vastly increased strength. The Iron Dominion started using the process of legionization upon their arrival in New Megaopolis in 3237. Microchips were also provided to the local Dark Egg Legion designed to de-activate the bombs placed in their cybernetics, but also render them completely susceptible to the Iron Queen's Magitek. After they successfully occupied New Mobotropolis the Iron Dominion began rounding up citizens and forced them to undergo the process of legionization. Legionized Mobians were subsequently dispatched to regional Dark Egg Legion chapters abroad.
Though Roboticization was later made possible once again as a result of Operation: Clean Sweep, only half the planet's population was left vulnerable to the process, and thus Legionization continued to be employed as a process of enslavement.