in the patch notes this is how the cards are listed
1. 1 star is a common
2. 2 star is an uncommon
3. 3 star is a rare
4. 4 star is a epic
5. 5 star is a legendary

Now as for building a deck in game the game counts legendary, epic, rare and uncommon as rare cards and will not let you put more than one of these in your deck at one time which in final fantasy 8 there was no problems intermixing these cards in your deck. in this game you are only allowed you are allowed only to use 4 common cards mixed with 1 of the other 4 choices which makes you ability to win maybe about .0001% especially against npcs that use only the random rule since there is no such thing as an npc with common cards except for teh one that you get training from first off.