Ofcourse .JPG is no file format I'd recommend for sprites, I'd recommend .PNG or even .GIF (if you wish to implement image transparency aswell.)
Otherwise you've done a nice attempt on the Moltres. However, your backsprite could use a bit of adjusting, try taking any backsprite from the GBA games and observe its structure; take note of the shades of colours used, how exactly it was shaded and how you could use the same kind of techniques on your own revamp. Basically doing the same thing as your Moltres.
Make sure you pick your colour palette carefully aswell, I'm aware that Crystal/Marina (or however you wish to call her) has no 32-bit sprite to use as reference, but it is worth a try atleast.
Hope that helps.