Robotnik was actually Tails the entire time.The ending to the Game Gear version sees Robotnik fleeing into a transporter, only to be replaced by a two-tailed fox. Coincidence?
Robotnik steals Tails' soul in Sonic the Hedgehog 2 - Game Gear.If you cheat to get to the last level instead of getting all the Chaos Emeralds, you get the bad ending (Sonic alone, Tails in the sky) EVEN THOUGH Tails appeared in the teleporter. The rescue didn't count for some reason, it seems. Why? Robotnik did something to Tails after capturing him (which is why he captured Tails alone and didn't capture Sonic at the end of Underground Zone Act 3), which did something to him; he Came Back Wrong. I think that Robotnik stole Tails's soul to power some kind of doomsday weapon. After rescuing the comatose Tails, Sonic carries him all the way home, tries to feed him some mushed up baby food, talks to him for a while, tucks him in bed, reads him a bedtime story, and watches over him all night and all day from that point, hoping he'll recover. DO NOT CHEAT.
Tails was originally guardian of the Master Emerald.Think about it. Tails was a replacement for Amy, who was going to be a "spirit" type entity that time traveled with Sonic to retrieve the Emeralds. However, he was changed into a Tanuki, which was dropped because of Tanooki Mario, then into a Kitsune (hence the two tails), which was changed into a fox for American audience convenience. Given this mystical background of What Could Have Been, coupled with his Chosen One status in the American comics, and the initial idea to give him latent powers in the Saturday morning cartoon, makes an interesting origin story indeed. Not to mention the scrapped Hidden Palace level had an end of level obstacle that resembled the Master Emerald, and the level had a Tails 1-Up monitor which lead those to believe it was a Tails only level.
Dr. Robotnik is secretly the real CEO of BP.
Tails was meant to be playable in Sonic 2 8-bits.
In the bad ending of Sonic 2 8-bit, Sonic forgot about Tails.The end credits scene is Sonic realizing he forgot to rescue Tails.
The Hidden Palace was always connected to the Mystic Cave Zone and was where Robotnik was researching more into the Chaos Emeralds as well as making preparations on the Death Egg.The 2013 iPhone/Android version has you enter Hidden Palace zone via what was once a dreaded spike pit in the Mystic Cave zone. In most timelines (i.e, most ports of Sonic 2) the entrance is blocked off by spikes as Robotnik knew Sonic would probably trail him here and block off this route to buy himself some time. In the new version's timeline, Sonic and Tails got there faster than expected before Robotnik could finish plugging the holes, thus they could get into the Hidden Palace where Robotnik was hiding. He had enough time to change its once hauntingly beautiful theme music though.