"I don’t see Sonic’s ability to use Chaos Control with a fake emerald as an asspull. He’s familiar with the energy from emeralds and remembers that Tails said it even has the same wavelength and properties even if it is much weaker than a real emerald." I have thoughts on this, and I've actually come to the opposite conclusion: the game's subtext appears to suggest that the fake Emerald might actually be slightly more powerful than a real Chaos Emerald. It's just that the characters are limited in their knowledge and therefore assume the fake is weaker, even though in-game evidence like Eggman's radar registering it as a legit Emerald would seem to point in the other direction. My take on it is that Sonic didn't pull Chaos Control out of his ass. Rather, it was the fake Emerald that saved him. First, let's consider how Sonic normally uses the Emeralds. He draws on the power of positivity and everyone's wishes in order to go Super. However, he confesses to Knuckles that he wasn't sure he could pull off Chaos Control. This would imply that his attempt at Chaos Control should have failed due to his doubt. However, if the fake Emerald didn't require the same degree of conviction that it takes for him to go Super - if it could take Sonic's dread-filled wish to survive and execute Chaos Control anyway, essentially despite Sonic and not because of him - that would mean its power potentially exceeds a regular Emerald's. Apparently the Japanese version says that the fake Emerald is designed to absorb the energy of the other Emeralds and explode. If that were true, then Sonic shouldn't have been able to pull off Chaos Control at all because there should have been no energy for him to draw on. What happened? Well, we could say Sonic has thick plot armor or something, but I think the likelier interpretation is that he accidentally activated the fake's latent power. So it might not have really been an empty sponge so much as a dormant sponge. The English version likens the fake Emerald to a battery by saying that it's designed to "reverse the energy field" inside the other Emeralds and blow up. This implies the fake Emerald has a higher voltage than the rest of the Emeralds, because batteries need higher voltages to override and reverse normal-flowing current. Shadow's disbelief at Sonic's ability to "activate the Chaos Control using an Emerald that's fake" also discourages the possibility of a placebo, because a fluke like that shouldn't be replicable. Meanwhile Sonic shouts "I'll use YOUR technique" so often you could make a drinking game out of it lol. Like, if the fake is powerful enough that Sonic's "ehhh idk about this" proved enough to save him from an explosion, imagine how much more powerful it'd be once he started actually believing in its power. (Or at least, his power channeled through the fake Emerald.) This could explain why he executes Chaos Control much more regularly and expertly in the final vs. Shadow fight.
That battery analogy...actually makes a fair bit of sense! It might explain why Shadow was so shocked. Because if he's used to the "natural" output of real Emeralds, encountering an artificial one that forces a polarity reversal would feel "wrong" or "fake" to him, even if it's technically more volatile and powerful than the real thing.
Sonic does look genuinely winded and a little loopy after doing it. Though you could chalk that up to him not being used to the sensation of Chaos Control than having to compensate for any lack of power in the fake emerald with his own.
This potentially does bring up something actually pretty interesting about Sonic’s character; He doesn't have the intricate understanding of the Emeralds that Tails or Dr Eggman do but he has perhaps an instinctive connection to them. Whether it's a battery or a dormant sponge, Sonic doesn't need to know how it works to use it, he just feels the energy and reacts instantly. It makes a surprising amount of sense that his "fake it 'til you make it" approach worked, not because he was lucky. But because he knew how to bridge the gap between himself and that kind of raw power.
