As I already said, it’s better to make 2 decks, a Light one and a Dark one. The creatures can be from tier 5, or all screenshots from the game, or fan-made (though there might be issues with copyrights here... but I don’t deal with that). The creatures should range from level 2 to level 7 with upgrades, from tier 2 up to the king. For the aces and jokers, you can use anything: either the castle of the race, or very powerful artifacts, or legendary heroes.
This is my personal opinion regarding such cards.