Scratch and Grounder are outcasts who WANT to be roboticized, so they can better inflict mayhem on their tormentors.

Doctor Robotnik was not uploaded here because he's not fluffy enough: https://www.deviantart.com/lgliang/.....ctor-794410499

Sonic / Tails: http://www.furaffinity.net/view/25499332/
Rouge / Knuckles: http://www.furaffinity.net/view/25624689/

Just a few more left.