First off, congrats on your first .gif! They can be daunting to make.
Now onto the gif itself. There seems to be some blur right around the time Hydreigon comes into frame. I'm not actually sure what's causing it, but making each frame bigger and re-animating the frames together might(?) fix this. That aside, it looks nice. Also, transparentizing the background might make it look better. There's not too much else to say about it, I think.