I would love to have some opinions about this piece please.
All advice is greatly appreciated. Thank you.

I think it's a beautiful piece! Personally, there are a few minor changes I would make. Blend the ground mist? on the left side so it fades off more as it rises.

I would also lose the dark branches that seen in the thruway of the arch.

Lovely job Ynys Hafod!

I think the biggest issue right now is the overall image quality. Everything is very grainy/pixelated which makes it hard to appreciate all of the little details. In general, this can be helped by working on a larger canvas size (I typically use around 1200x1800 px). In this piece specially, I would recommend removing the snow because it adds to the graininess and obstructs smaller elements.
.

As a whole, I think the concept is super cute and you've put the image together very well!! I really like the grounding of the horse and the fox looks very natural. Keep up the great work!