Honestly, I can't find anything to nitpick at. Generally, when people shoot animals, they try to fill the frame with their subject. This could be a wonderful landscape photo, the pop of the running reindeer (I think that's what it is) really captures the viewer's attention.
Your decision to add the rocky foreground adds depth that the two-deimensional photos lack. It's awesome!
I love the color pallette here, too. Normally I'm attracted to deep tones and rich colors, but there's something soft and comforting (to me, at least, haha) about the muted browns and greys in this photo.
All in all, it's a wonderful and unique photo. You've gained a watcher for sure!
From what I know of deer, Stag and other similar such creatures, they are timid, nervous and run at the slightest noise. The fact you managed to capture it, clearly with style and such sharpness is outstanding.
I can see nothing at all wrong with your shot, you got the focus perfect between the rocks and moss, and the stag perfect. I especially love the background focus of the lake. Can I take a guess and say this is somewhere in the Scottish Highlands...?
I love the colour too, and the landscape in general, very well done!