I think maybe you should work with tiles instead of sketching out and filling in this large of a background, so I'd scrap everything besides the refined left part of the sketch and work from there. The stuff you laid in in the back isn't going to stay in any fashion, so it's just distracting.
The underwater part is a neat idea, but you aren't really adding anything new to it that the last person who made a mockup like this had. The highlights on the grass strands you have right now need to move more to the yellow side of the color chart, while the darker parts need to be much bluer.
The health bar in the corner looks fine to me.

Overall I feel you're sticking to closely to what has already been made; bring some of your own stuff to the mix, whatever it may be.

You forgot (?) the skull capeholder dealy he had in the sketch. I like the helm design, very neat. Of course PK's edit rox, but I think that would be much harder to animate so I wouldn't add as many folds in the fabric.

The size depends on what resolution you are going to use. Capcom sprites are under half the size of this, but Guilty Gear's sprites are roughly the same size I think. I'd adopt the 50% approach; this could take a while to color and animate properly at this size. Based on the older sketches I saw I think this character design is stronger than what you had but is still sort of bland. Consider my 'significant accessory' theory. :3

It looks like to me that the arms and torso are way too long compared to the length of the lower body. I don't think the problem is so much that the upper half is too long as much as that the lower half is much too short, especially if you're going for a sort of lanky look, which I assume you are. The neck looks really overly long also. The metal sheen looks much better than it did before, excellent job on that.

Nah, I was thinking the same thing about the face and I figured it was because I'd been looking at it too long, you know? I didn't apply all of your facial edits to it so I could still do those, and if it is still wonky I'll switch the colors up some. That should be fun. :3

Outsponded by lonlaz! Adding more for great justice.

At first, the character was a guy, but when I had finished the first go everything looked very feminine. The pink certainly doesn't help that. XD So I just decided to leave the sexuality of 'Nemo' up in the air, although he is just a very pretty boy I guess. Thanks for the reply.

Edit: I should also add I'm making this for the enterance page for my website I'm making, and it will be displayed on a plain white background. I'll also be adding a cat, but first things first right?