When asked if Sonic 2's time travel idea was created before or after Sonic CD's time travel, Yasuhara said "I didn't know what Ohshima-san did at the time". (07m 05s) Famitsu's interview for Sonic's 25th anniversary had this exchange: https://sonicjpnews.blogspot.com/2016/06/translation-of-sonic-25th-anniversary.html So if Ohshima's memory is accurate, Metal Sonic had already been designed by the time he heard that Sonic 2 would have a Mecha Sonic. More recently, Yasushi Yamaguchi had this to say, when asked if there was a common origin between his Mecha Sonic and the Game Gear Mecha Sonic: https://twitter.com/judy_totoya/status/1595242576424349696 Google Translated: It's possible that's how they both landed on time travel. Naka mentions that was one of Ohshima's early ideas before Sonic was Sonic: https://shmuplations.com/sonicteam/ As for the Sonic robots, I think that just comes from it being the most obvious idea for what to do in a sequel. The evil twin character is inevitable, and when the series is all about fighting robots, then of course the evil twin is going to be a robot. And in Japan the most obvious name for a robot Sonic would be "Mecha Sonic".