Sonic the Hedgehog 2/WMG
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.
- Perhaps the Chaos Emeralds give Sonic the ability to restore Tails to how he was... or give Sonic the ability to locate Tails in (or enter) the Crystal Egg zone; without them, Sonic can't pursue Robotnik and the game would have to end there.
- The level select screen represents Sonic looking around all of Mobius at random. By the time he gets to the Crystal Egg zone by some other means, it's too late for Tails.
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.
- The oil spill in the Gulf of Mexico was another of his evil schemes to recreate the Oil Ocean Zone.
Tails was meant to be playable in Sonic 2 8-bits.
- Even though he's supposed to have been captured by Eggman, Tails still appears with Sonic in all title cards. Also, as seen in the game's good ending, Tails has an almost complete spritesheet. The development team probably didn't bother to change the title cards after dummying him out.
- I think it becomes a bit of Fridge Brilliance if you consider that Sonic is desperately wanting Tails to be at his side, and the title cards are Sonic remembering the fun times he had with Tails the last time they were in the Zone together.
- Actually it's even more Fridge Brilliance if you think of the 8-bit game as Robotnik's revenge against Tails for defeating him alone while Sonic was stuck in Sonic CD. Now that Sonic CD is moved in the timeline, the Tails Alone modes of 2 and 3&K never happen, therefore Sonic AND Tails venture through Sonic 2 8-bit like they should have!