Sonic's first shown appearance in a video game was in the 1991 arcade racing game "Rad Mobile", as a decorative ornament hanging from a rearview mirror. Sonic's first playable appearance was in the platform game "Sonic the Hedgehog" for the Sega Mega Drive/Genesis, which also introduced his nemesis Dr. Robotnik. His two-tailed fox friend Tails joined him in the game's 1992 sequel, "Sonic the Hedgehog 2". "Sonic CD", released in 1993, introduced Sonic's self-appointed girlfriend Amy Rose and recurring robotic doppelgänger Metal Sonic as Sonic traveled through time to ensure a good future for the world. "Sonic 3" and its direct sequel "Sonic & Knuckles", both released in 1994, saw Sonic and Tails battle Robotnik again, with the additional threat of Knuckles, who is tricked by Robotnik into thinking Sonic is a threat. "" (2010–2012) continues where the story of "Sonic 3" left off, reducing Sonic to the only playable character and releasing in episodic installments. The second episode sees the return of both Tails as Sonic's sidekick and Metal Sonic as a recurring enemy.