Lineart on this is great, P_A_D, excluding that big tusk there. It just looks really oddly positioned and throws all sense of perspective on the sprite. The colouring is pretty saturated and has low contrast. I'd say you should try out some official colours, such as Rhyperior or something like Wishcash? The white highlights feel out of place and in some places it seems like there is
too much shading which just makes it look bad. The excessive amount of dithering doesn't help, either. Also, if it's a Pokémon sprite, then I'd like to point out that the light source in the Pokémon games is the top left, not top right. Still, it's pretty good, Poke_a_dialga!
Like Spherical Ice said, the light source is on the top left. The shading isn't really in Pokémon's style, usually Pokémon sprites are shaded with only two colours, the base colour and a darker colour. Look at the front arm for example, you have a white highlight, the base under it, a darker colour and an even darker colour. You also use a lot of highlights which also isn't similar to the style.
Double-reply~
For some reasons, I had the feeling to sprite it like that @@
And thanks for the advices (urgh... it's been so long since I last check this place eversince I transferred schools =='l")
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I'm having my winter break (AT LAST!!!) and I kinda have some updates.
After I transferred, I had no choice but to stay in the dorm. There ain't any computers in the room, so I couldn't do much. Whenever I return home during the weekends, I had to relax myself up for the week. And ignore these stuff and let's get back to the topic:
I've sprited some fakemon and drew a dragon (say YAY XDDDD)
Ok... not the whole dragon yet... I've only finished the head and neck...
Those 2 parts alone took me the whole afternoon's time @@

Grassalo
(It's basicly the improved version of my previous sprite~)

Erafire

Croafire

Eragon

Dragon
EDIT: Updated
Dragon with body. I don't really like the body that much and it's currently not the final design.