I asked Falgaia/aXl if I could try to do a Greninja with a custom pose and this was the result :x
I still have all the sprite parts of it but I'm sure someone can fix it up x3x
Edit: Oh and I'mma tweak the sprite a lot but I posted it here for feedback and stuff :x
You have a pretty decent base going for you, but there's still a lot of work needing done with this sprite. The most apparent flaw is the huge size of the tongue - while the part that wraps around Geninja's neck is fine, the part sticking out is dramatically over sized comparatively. Additionally, there seems to be many sizing issues throughout the sprite.
-Greninja's left (our right) leg looks as if it's a stub. I realize that this is just the angle the sprite is trying to take, but it needs to be executed better for us to be able to see the leg/foot clearly.
-Greninja's head seems to be somewhat lopsided to me - mainly due to the very top portion of his head. There needs to be a much smoother transition from the top of the head to the sides.
-Greninja's left (our right) arm seems to have some sort of an identity crisis. The shading leads us to believe that Greninja is holding his arm behind him, though the size doesn't transition that way.
Apart from sizing issues, there are some things I feel I need to nitpick at:
-Greninja is missing the white mark above his eye.
-The center fin on Greninja's head just seems to be slapped on, and doesn't really transition too well in my opinion.
-The shading, while not completely pillow shaded, does have a lot of pillow shaded segments: the stomach, tongue, and white joint "bubbles" all seem to have a repetitive shading technique that doesn't follow a normal lighting.
-The fin/tail on Greninja's underside looks a little...suggestive to me. This only became apparent after staring at the sprite for a while, but is definitely something that needs touched up.
Ultimately, it's a decent sprite that has a lot that can be improved on. But in my personal opinion, I feel as if Greninja lower on the list of priorities for this project, seeing as we have multiple sprites to work with him as is. Though I'd definitely encourage you to try to fix up the sprite just to hone your skills more. There is potential to be seen. :)