A character's stars represents the level at which the character is at and is located below the character's art when viewing the card. A character can have a minimum of 2 stars or a maximum of 5 stars at their final level. Each star represents an 'evolution' of the character and the card's power and/or damage will increase with each increase in stars and their artwork will change. Also, abilities may be unlocked depending upon how many stars a card has. Also, certain rooms have special formats that involve how many stars your deck involves in total. This is basically the sum of the star count of all of your cards.