Playing cards based on Heroes of Might and Magic.

Or maybe you could divide the deck into dark and light factions, meaning Hearts and Diamonds are light, while Spades and Clubs are dark.

There won't be enough creatures. And even less for alt-arts... To fit all 168 creatures, you'd need 4 decks... And even then, they wouldn't fit properly. Besides, many fan-made illustrations are generic for both regular and alt-art versions, so you could easily use that large red Landlord as the first alt-art.