This is an alternative art for one of the cards in the game ("Sea of Blood"), that is going to be awarded on one of the upcoming Game of Thrones world championships, courtesy to the Bulgarian national team. It will also be a playmat.
The concept is based on a paragraph in one of the books, and depicts the coming tides of the Dothraki cavalry as a sea (and is using the colours of the Bulgarian flag).
(sketches included for fun).