Sonic the Hedgehog 4/Fridge

Fridge Logic

 * Regarding the Old Save Bonus, Episode Metal. While the idea of Metal Sonic being playable is cool and all... Why the heck is he fighting his own boss? He didn't betray Eggman yet, did he?
 * That would imply that he is fighting Eggman. We know nothing about the game except "Metal Sonic's playable! Weeee!"
 * The Episode Metal campagin has no boss fights.
 * And for all we know, the Badniks Metal Sonic faces could probably just be in his way, and Eggman doesn't care what happens to them.
 * Well, those Badniks of his DID let the real Sonic get through them, so...
 * Again, about Episode Metal... The trailer revealing it showed Metal Sonic, broken, in Stardust Speedway as he should be. There is one problem with this picture; Stardust Speedway is in it's Bad Future. That is contradictory to what actually happened in Sonic CD, is it not?
 * It's never really been said which ending to Sonic CD is canon. In fact, the entire purpose of Episode 2 is to show where CD fits in.
 * Besides, Sonic the Hedgehog 2006 was supposed to have been erased from the timeline, and yet Crisis City still made it into Sonic Generations. Granted, the events of that game was due to, but still.

Fridge Brilliance

 * Why does Sonic have the homing attack here? He learned it from himself!
 * An alternate theory from here: The Homing Attack is a side effect of turning Hyper Sonic in the last game. In fact, look at the Chaos Emeralds; they're way bigger then in games further down the timeline, like Sonic Heroes or Shadow. They're still powering down from the power boost they got before. Which explains why Sonic's super form conks out in combo moves: they're not stabilized yet.
 * Metal Sonic obtains incredibly great power during this game, which he flaunts during his boss fight, but why doesn't he use it in his playable segments? Aside from Gameplay and Story Segregation, he's saving this power for when he fights Sonic again.
 * Badniks aren't exactly great challenges on their own, and even in groups they'll give moderate trouble at best. Metal Sonic has proven himself to be rather arrogant, and since his mission is to terminate Sonic it's likely that he is the only one Metal could possibly consider his rival. Therefore, he wouldn't waste his time and energy using his powers on the slow, clunky Badniks, but rather save them for when he has the world's fastest hedgehog to contend with.
 * It was said that Episode 2 would bridge a gap between Metal Sonic's appearence in CD and explain how he showed up in Heroes. At first, you see no allusions to Heroes, but then you realize that this isn't meant to be direct link; this is meant to set up Metal Sonic's slip into madness. The best technology at their disposal, the strongest mystical energy they can find without resorting to Chaos energy, all weaved into his chassis, and he still can't manage a fight with Sonic. Add in the fact that someone even stronger than him showed up and allowed for such a close bout than the Doctor had gotten with Metal, and the mix of power corrupting his system, burning hatred, and a possible inferiority complex would eventually cause him to turn on his creator.

Fridge Horror

 * Assuming the Stardust Speedway seen in the intro of Episode Metal is canon to Sonic CD as well, it appears Sonic failed in saving the future of Stardust Speedway. That, or Eggman took it over using the Little Planet's bizarre chronology once again.
 * What if he claimed Metal Sonic and they left the Little Planet before time re-organised itself?
 * If Sonic had saved Stardust Speedway, Metal Sonic would have been defeated in the Good Future, with the Bad Future being untouched by Sonic as it never happened. That said, if time needed to reorganize itself, it would have been instantaneous in that case, Bad Future Metal Sonic would have been just fine... Alternately, Little Planet getting a Bad Future might have been a side effect of Time Eater's meddling, and since Sonic defeated Metal Sonic there too, your possibility opens up.