Vintar

Since you asked me for a critique, I will give it a try. It's my first, so bare with me. Haha.

To start off, I like your idea for the manip, and the chosen images are nice.

I'll begin with some details about the horse. The cropping is a bit off some places, which means that you've left some spots out, and it seems like you have used a tad harsh brush. I would have spent more time on the cropping, as that is important to make the horse blend in.
The next thing that I see, is the colors of the horse. The background is very green, and in this case, I would try to match the horse a bit. Play around with the color-settings, aswell as the curves (to make it a bit darker, the bg is pretty dark).
What I think is good, is the lightning, it looks right. And the mane/tail looks really good! <img src="e.deviantart.net/emoticons/s/s…" width="15" height="15" alt="" data-embed-type="emoticon" data-embed-id="391" title=" (Smile)"/> Nice work on the eye, too.

As for the background I don't have that much to say. It's a gorgeous background.
The splashes, though. They're too white/bright. Again, a re-color and maybe lower the opacity a bit, would probably do the trick. And remember that even though the horse is in movement, I don't think there would be that high splashes, if we should be realistic. But the splashes looks great, very realistic!

What I think would be nice (that's rather a tip than critique) is to blur the background a bit, so only the front is all clear. It gives more focus on the horse, and I think that's really pretty.

Other than that, I think you have a really good technique, but you need to focus on spending a little more time on your details.
Good work in general! <img src="e.deviantart.net/emoticons/s/s…" width="15" height="15" alt="" data-embed-type="emoticon" data-embed-id="391" title=" (Smile)"/> Keep it up!