Great idea, there is an Arthas version mounted HD, but with Knight animations, I think it's a good alternative too, although I like LordG's horse.
I have some small considerations, which does not interfere with anything in the final quality and the great work: Unfortunately the armor on the right side of the chest was a little too stretched using the Garithos shape, in addition to not wearing a cape either, its absence compromises for Arthas a little. I think the cloths at the base of the horse could accompany the use of the TC, not turning white. The model lost the dust trail in the "Walk" animation!
I thought the idea of inserting the open Book in "Spell" was great, although the edits are still a little rigid.
It will be useful for many, congratulations!