So I went ahead and removed all shading from the sprite. Now based on the HDBZ sprites:

It looks like the light source would have to be in the Upper right corner. (Think so, I'm bad with shading )

Now you have to think about the lightsource. That light on his stomach has to go, or if anything it needs to be fixed. The lightsource comes from above.

It seems you still haven't checked the sprites Balthazar made (why?!?), so I compiled a little spritesheet for you:

(only those that could be helpful)

They might need an update seeing how the style evolves, but they could be a great reference.

I'd make his antennae a little thicker than just being 1 pixel thick lines. You know, like in the EB sprite:



I cannot help but to think his shading overall looks pretty basic. The EB sprite could serve as reference on how to handle the shading and contrast on your sprite.

There are literal kaio sprites inside Ssj Goku, why not base off those instead of making a first frame from scratch? He appears in 3 winposes. "training winpose" , "car crash winpose" and "riding with goku" winpose.

Gotenks is almost too small in game. Smaller character can pose issues. That's why I suggested making him a bit bigger.

I'd make him slightly bigger so he doesn't seem shorter than Gotenks in game

On the standing animation, before caring about the antennae would you see him moving like that?
Remember, moving parts of the sprite up/down and left/right usually doesn't give you the final product, you should always adjust everything.

Also, is this the size of the sprites you're going for? I saw you wanted to make him Z2 so you would need to make it bigger.

Before looking at it closely I thought you were using one colour for his skin. That's because of bad contrast.