Buying Treasure Cards in the bazaar displays a "set" parameter.
I recently found three different "sets" of Nature's Wrath cards in the bazaar. Other than having different "set" symbols and different prices based on their differing quantities, all three "sets" had the exact same card in respect to card performance. All three "sets" were acceptable to the recipe I was trying to craft.
You can buy a pack of treasure cards with crowns from the Crown Shop (the crown icon on the upper left of your screen). You get random cards from the various sets. I've not noticed any significance related to the set name.
The two main Crowns Shop sets are Eye of Bartleby and Marvenlous Minions. The former has a picture of Bartleby (though it looks more like a mushroom), and the latter a picture of what I guess is a minion's head and hat.
I haven't seen a difference between the generic treasure card and the Marvelous Minions set card. The Bartleby card generally adds another 5% to the accuracy of attack cards, 5% to the attack power of blades and traps, and 5% to the damage reduction of shields.
