Make a Hue/Saturation adjustment layer (set as Clipping Mask) to desaturate the deer. Bring the Saturation values down to -79:
Add an Invert adjustment layer to invert the color and contrast of the deer. On this layer mask, paint on his upper body and the back of his legs to reveal the original effect there.
Create a Color Balance adjustment layer and alter the Midtones settings:
Make two Curves adjustment layers to reduce the contrast of the deer. On these layer masks, paint on any details you feel too hazy to reduce the effect there.
Add a new layer, change the mode to Overlay 100% and fill with 50% gray.
Activate the Dodge and Burn Tool (O) with Midtones Range, Exposure about 10-15% to refine the light and shadow on some details of the deer. You can see how I did it with Normal mode and the result with Overlay mode.
Make a new layer and a small brush with the color #5d7685 to paint a missing detail between the hind legs of the deer.
Create a new layer and use a small brush with the color #98bed0 to paint more fur around the tail, body,legs and head.
Make a new layer and use the same brush to paint two horns above the existing ones. Use a small brush (about 6-7 px) but it depends on the size of your document.
Add two layers and use a small soft brush with the color #d1d9dd to paint a highlight on the deer's body, head, and horns. Change these layers mode to Overlay 100%.
Add a new layer and use the same brush to paint more light around the deer's head. Alter this layer mode to Soft Light 100%.
Create two layers and use the same brush but increase its size to paint glowing light around the deer. Change the first layer mode to Overlay 100% and the second to Soft Light 100%. Use a layer mask on each of these layers to refine any unwanted details.
Make a new layer, and a small brush with the color #648da0 to paint some tiny darker details on the horns.
Isolate the leaves from the background and take different leaves to add to the deer's horns and around the scene. Use the Free Transform Tool (Ctrl+T) with the Warp mode to make the leaves appear different.
Add more bigger leaves to the scene, especially the edges and on each of these layers, go to Filter > Blur > Gaussian Blur and set the radius to 4 px or 8 px (it depends on the distance from the viewer to the leaves to create a depth for the whole scene).
Select all of the leaf layers and hit Ctrl+G to make a group for them. Change the group's mode to Normal 100% and make a Hue/Saturation adjustment layer within this group to change the leaves' color:
Create a Curves adjustment layer to brighten the leaves. On this layer mask, paint on the hidden side of the leaves or any details you feel too bright.
Make another Curves adjustment layer to darken the hidden side of the leaves a bit more. The selected areas show where to paint on the layer mask.
Create a Vibrance adjustment layer to enhance the color of the leaves. On this layer mask, paint on the leaves on the horns and some leaves around to remove the effect there.