I feel that the main issue with your graphic is the rotation of the diagonal view. There are a few tutorials on rotating pixel art in this thread (maybe check the second page) on the official Graal forums and I suggest you check them out. Like Dusty states in that thread though, in order to come out with a better outcome, your best bet is to just put the effort into actually drawing the other sprite. You're always going to need to redraw the sprite (whether its tracing over it, cleaning and then detailing, or completely drawing it fresh and using the rotation as a reference) in order for it to look good.