Ok, so I know it's a bit late but here's my review of the skin:
First of all as always I'll start with just some general comments as well as the positives. We have two more amazing skins here from Shido that completely transform Lord Garithos into either an avatar of the cold or an avatar of flame and lava. As someone who has worked with this skin before it can be a bit tricky (mostly due to size and the sheer amount of things to work on) but is generally one of the better ones in terms of wrap. Therefore props must be given to just how well Shido has turned an original vanilla skin into something completely different in their own trademark style of bold cartoonish colours as well as very competent detailing. The colour choice (whilst obvious) is very good for conveying either cold or warmth. I'd like to give special mention to the shield which looks amazing as well as the reigns which can be tricky but Shido has turned into a cool stretch of fabric with diamond shaped pendants hanging from them. There's frankly too much here to comment on without becoming repetitive without just saying [x] is amazing or [x] looks really good. Just as a note I will state that the skin appears to be 97% free-hand which is always appreciated. Another thing I will say is I like the changes made to the head and face which is an area often neglected in skins like this and I am especially fond of the glowing eyes and saddle parts. Also the manes' look amazing.
Now for criticisms and any other comments. I should really call this the "nit-pick" section since everything I'm about to say is really minor and the skin is truly really good. There isn't really much to say. I do wish you'd done something a bit more inventive with the horses armour particularly on the neck. It's been re-drawn but looks very similar to the original. I look at the quality of the shading on these parts and then I look at the tabard and feel like the tabard looks just a little flat and could maybe use just a touch more detail to make it look more fabric-y. The hair on the coldheart texture doesn't look as good as his warmer variant but I think that's just due to the difficulty in working with such a bright/light shade of colour.
Other than that, I've got to say this is another great addition to the skins section and I'm looking forward to seeing what you come up with next as it's always something I didn't expect (I'll also need to find an excuse to use the warm variant texture maybe for something Ragnaros related somewhere). My nitpicks do not prevent me from giving this a 5/5. Well done Shido!