Very pretty visuals; highly evocative of Hearthstone! The wood texture in the background is especially good, and the board/playing area is very cool! The game is very strong graphically, even without considering the 72-hour time limit!
I did get confused by the current "set's" territory though; the symbols on the board are very easy to miss. I feel in this situation the symbols should probably be the same color as the current territory to allow it to be easier to read at a glance, or that color should be represented somewhere on or near the board.
Speaking of which, I think the cat's and orc's colors (orange and red) are somewhat too similar when placed on the board. I got confused the first time the opponent placed a cat card and I had no cat cards, so I placed a high-level orc card thinking it would win (it did not).
The game itself is mostly balanced and easy to grasp, which is much to your credit! I won my matches against the ai, so it's difficult to determine how it would feel to play against a human player, but the strategy seemed simple enough to comprehend for a beginner like me.
That said, there seemed to be a few things I wondered about or was unsure of: - It wasn't clear to me how the cards were being distributed to each player. The tutorial says that 36 cards are available, but only 18 are in play for each set (9 for each player). If this is the case and not every card is in play during each set, it's difficult to know what cards your opponent has, and therefore it's difficult to form a strategy based on what you suspect they will play. - The connection between the strength of a card (its number) and the value of the card (its "coin") doesn't seem to have any intuitive connection. This makes it hard to make any strategies around which cards to keep and which cards to sacrifice.
Other minor things such as the game seeming to cut off some elements in certain screen ratios, or the inability to hover over cards to see their details (name, coin) are present, but don't hinder the gameplay experience much, if at all.
All said, this game is very, very impressive considering the time limitation! You have a working ai opponent that managed to stay a step behind me throughout each set, very clean and beautiful ui/graphics, and simple and easy-to-learn gameplay! Well done!