You've discussed before how the 2D platformer standard of jumping on enemies to attack them doesn't work as well in 3D because it's so much harder to line up. This is why Mario keeps getting extra moves like Galaxy's spin attack, and why Sonic got the homing attack. But Sonic already had a move in 2D that expanded his attack hitbox to make it easier to hit enemies: The Insta-Shield from Sonic 3. Do you think that would have worked in 3D, or would it still be too fiddly?
The InstaShield, as it appears and functions in Sonic 3, would be difficult to work with in 3D. It’s still kind of the Castlevania Whip problem.
This whip draws a straight line in front of the player, and anything that intersects with that line takes damage. It functions almost like a laser. But in 3D, suddenly it becomes super easy to miss when all you’re doing is drawing a straight line in one direction like that.
Why Super Mario Galaxy works is because it’s a sweeping motion. You are effectively doubling the size of Mario’s hitbox and saying “while spinning, anything that touches you from any direction takes damage.” It’s basically impossible to miss with that attack, unless you’re too far away from an enemy.
I don’t think this applies to the InstaShield for several reasons. For starters, personally, the InstaShield always read to me as a Castlevania “line” attack.
Now you could flip that on its side so that you’re kind of whipping a ring of energy outwards (instead of forward), and that would work, but the other problem is that the InstaShield requires you to be in the air when you do it.
In terms of being intuitive for players to use, the idea that you’d have to jump to use your AOE sweep attack is a little awkward. Because now you create a problem where you’re above most enemies you’re attacking, or you make the enemies so big that it’s only logical you’d jump up in to them.
Because you look at the spin attack in Super Mario Galaxy, or Crash Bandicoot, or just melee-focused games like Bloodborne or even Skyrim and they’re all ground based. Certainly those games let you attack out of a jump, but it’s not the only option. Jumping is not a required step to attacking.
Okay, so you make the InstaShield usable from the ground. Well, Sonic uses his ball state for jumping and rolling already, and now we’ve got a new, separate attack state that’s different from both of those that also switches to ball state. How is that clearly different from rolling? Is rolling required to use the InstaShield first? Can you roll out of an InstaShield? I feel like it starts to muddy the waters.
So then you break this all down to its fundamental actions and it’s just an AOE attack that doesn’t have to involve spinning in to the ball state. Now you’ve just literally given Sonic the spin punch attack from Super Mario Galaxy. But is that necessarily very Sonic-y? Sonic has certainly used his fists in games before, but he’s never really been known specifically for punching.
As you can see, you can very easily fall down a rabbit hole of “Why does it need to be this way?” This kind of nitpicking can be what separates the good games from the truly great. You want something that feels organic from both an aesthetic and a mechanical perspective.
I’m also not generally a fan of the InstaShield anyway. It was more than ten years after Sonic 3 released that I finally started to grasp how to use it properly. It is, by its very nature, not intuitive at all. It’s just this thing you can do, and it’s never explained what it’s for or what enemies are susceptible to it or anything. Here’s literally all the manual says about it:
It never made any sense to me, because in that context, having a flash-shield seemed pretty useless. It wasn’t until the era of being able to pull up a Youtube video that I could see how other people played the game and realized the InstaShield’s true function. And even then, for 90% of the game, it doesn’t provide any actual tangible benefit over just attacking normally. It’s mainly useful for spiked enemies and not much else.
Trying to make it relevant in a 3D Sonic game just doesn’t make any sense to me. It’s up there with Sonic CD’s “Super Peel-out” as being something that’s ultimately kind of pointless but people hold on to it anyway just because it looks cool and they have nostalgia for that.