Sprites + visual flair.
So his sprites are really well done, along with animations. Both of these things are pretty simple, but they somehow manage to actually work really well together, like it just looks really cool to me yet I can't point a single reason why, so I'll just point out all of them. :P
1. The fact that the sprites are actually scratch vectors. (And about that... check your scratch account's notifications. >:3)
2. The simple, almost shadeless sprites with the geometric-esk look works really good together which gives the sprites a very specific clean look,
3. His animations look simple in the best meaning of this word, a good example of that is his jog animation, which I also really like. :3 It just has a nice energy to it.
4. Rayman body type perhaps? I feel like there's not a lot of characters with disconnected limbs, so it maybe makes him more special? (Still really cool)
And for the visual flair. (This is more of an audio flair, but) I really like the footstep sfx, not sure why, but it just sounds really good to me, probably because of the bit-crunch. And while I'm talking about audio, his custom movement sfx also sound pretty good, they give off a sega master system vibes, which is pretty unique I feel. And the music selection is also pretty neat, I mainly like the invincibility theme.
And for the actual visual flair, the dust clouds while running are a cool addition and the double jump air ring gives off a modern feel if you get what I mean. And if you are able to do it, then you could add a vertically flipped air ring for the air-dash ability. It would give the move some more force behind it and it also would look much cooler this way. So something like this:
(But vertically flipped so it would look like he boosts through air making it scatter from the force. If that makes sense.)
Movement and other stuff.
So his moveset is in the category of being simple, yet made to be chained together, which also supports the huge control you have over the moveset midair like being able to use any move you want in almost every scenario as long as you haven't used up the move yet.
And I found some oddities that you might want to look into:
1. Holding spin while rebounding makes you constantly dash into the wall. - So from what I can gather, then it seems that you're able to dash instantly as long as you hold spin, which sometimes works in your favour, and sometimes doesn't, for example:
You can dash instantly after double jumping,
Yet you also can lose all of your rebound "charges" if you hold spin when rebounding.
So I guess you maybe could just make it so the dash works only if you press spin instead of holding it. Not sure how though. :C (Not even a raw idea surprisingly...)
2. So people weren't lying when they said that he's a bit op. I'm not sure if you honestly should change these things, so I'm just giving idea if you DID want to make him more balanced. So:
-You can double jump only once when your bounce charges are out, so you won't be able to "climb" the walls.
-Make the dive add only 10 fracunits to your speed to make his acceleration a bit less sudden, which also could make his spindash higher in value due to being able to accelerate faster and in less distance. But it seems that he can't rebound that well with only 10 fracunit speed, so you maybe could make it work like thok in Xmomentum does, so the base speed is 20, and you can build your speed higher every time you dive. Or you maybe could change the base dive speed to 15 fracunits instead, it makes the rebound a bit faster while still being less powerful when used in building speed.
3. For some reason you can recharge the stomp by pressing jump, even though it doesn't seem to do anything special like being able to double jump.
And just like the dive, the stomp also doesn't seem to have a cool down which causes this to happen. :P
So for context, the drill sounding thingy is caused when you hold custom1 and jump together, which both uses and recharges the stomp at the same time constantly, and the spring is pretty much the same, but without holding jump. So maybe give the bounce a cool-down or make the bounce normally rechargeable as a regular feature, or both.
4. The dive rebound works all around the character, so you get rebounded even if you touch the wall with your side, or even your back, which is kinda jarring sometimes. But I feel like this could help you iron this thing out if you're able to work with it.
A wall check that is from Source Code (maybe most of it) with some slight changes There are example hooks included to show if you are touching the wall.
mb.srb2.org