I've seen a bunch of Greninja fanarts around deviantART for some time now, and this looks outstanding coming from the use of tradtional tools.
The first thing I noticed is the background. It represents the time of ninjas back in Japan and this fits the Pokemon's appearance. The art techniques he uses are well done and I like how you can see the strokes to show wind.
From what I see in his gallery, he's definitely have a variety of drawing styles whilst keeping the roots of his colouring in the work. Overall, this is impressive and definitely captures the Pokemon well. Keep up the good work!