Oh! The nostalgia of a new generation! It's not hard to tell why Fennekin is such a crowd favorite. The little guys a super fluffy fox that breathes fire. Though in this image I can see some resemblences to zorua and eevee.
I really like the warm colors you used for this artwork and contrasted it with violet and indigo. It's well focused on the subject and the firespin doesn't distract from it. In fact the firespin has great movement, balances it out, and guides the viewer's attention across the entire image in a structured manner.
The triangle sparks by Fennekin's mouth look too sharp and could be softer and more curved. Other than that it looks really good.
Well, needless to say, I absolutely love this piece. It's actually my current phone background, and one of the better of the Fennekin fanart I've seen. I like the style of this, with the sharp edges on the Pokemon itself, and the softer, warm colors on the ground surrounding it. Fire Spin (I assume) looks just amazing. I really love the way you draw fire, especially how there are some little flecks of flame coming off of it. It almost looks like lava in some places, which I really think adds to it, making a cute Pokemon seem really badass and intimidating. I would suggest that you make the illuminated part of the ground reach more towards the bottom of the page, seeing that the Fire Spin would illuminate that area. I also feel that the "ear hair" shouldn't be as sharp looking, and be textured more, and so should the tail. The tail looks like a solid mass, so maybe some lines for texture wouldn't hurt. Besides those minor things, I genuinely enjoy this piece, and wish you the best in your future endeavors as an artist. I can't wait for Gen 6, and I also can't wait to see more from you as an artist.