I didn't tried the online features, but gave it a go on single player. The character art style is great! I really like how you did the 2D head, and the 3D body mixing well with each other. The animations and expressions are very good.
On the movement side, it felt like a mixture of Mario 64 with 3D Sonic. Quite an interesting choice. I really like the momentum mechanics that you added, like running on the walls, and having acceleration on the character when you try to stop. Also running on the loops. Although, when I touch the sonic speed boosts to get into a loop, If I tried to steer the character, I would often fall. I had to let go of the stick and let it auto pilot me, which is not as fun imo.
I noticed that when walking arround, I felt some kind of jitter. I don't know if this is due to the online code, but it can be due to Godot Physics. I had a similar problem, that was fixed by instaling Godot Jolt physics engine.
The camera would some times get stuck on walls or on the floor.
Speaking of the camera, there were some parts, like ascending bob-omb mountain, where the camera would try to reposition in a specific angle. I get what you are doing with it, but I felt it was quite disorienting. Perhaps it would be better to always let the player have the control, except on some sections like the 2D section. And when you take the control away, take it fully. Don't let the player control the camera at all.
The "jump poles" seems like a great idea, but right now they work in a very wierd way. I could not make them work, as I would often miss the direction I want to jump, and repositioning in the air was very dificult. One thing you could do, is make the air control more lenient.
On Emerald Coast I would fall onto the water, but clip under the level, and had to go down and respawn.
I was able to catch 13 of the 17 goals.
Overall, fantastic demo. It show's a lot of promise!! I'll be following the progress.
Also, you did a bunch of things that I need to add on my own game, like climbing poles, sliding down slopes, and having that "break effect", when suddently holding the oposite direction you are running. Can I persuade you to teach me how you did some off that stuff?