When you receive a card you already own, it becomes a duplicate. The number of duplicates you have is shown as a counter on the card.

• Duplicates convert into duplicate stars based on the card’s rarity (gold cards give double stars).
• You can spend duplicate stars to buy Duplicate Chests.
• You can send duplicate cards to your friends, except for gold cards which cannot be sent.
• You can send up to 3 duplicate cards per day. If you reach the limit, a cooldown timer will show until midnight server time.
• If you don’t have duplicates of a card, the send button will be disabled with a message explaining you need a duplicate to send.
• You can only send duplicates to friends who have the Collection feature unlocked.

When you receive duplicates from friends, your duplicate stars balance increases accordingly.