Coupons are used to draw 2 - 5 star creatures via the altar. 

Coupon shards are awarded by completing daily tasks. The shards can then be exchanged for a coupon. It costs 6 coupon shards to get a coupon. 

On February 8th 2017, in a run of 300 coupons the ratio was: 0,67% 5star, 6% 4star, 52% 3star, 24% 2star, 8,33% 3star essence and 9% 2star essence.

You can also get coupons by sharing your newly acquired 4-5 stars creature cards or 3-5 stars Hero cards on Facebook. The same is possible when you Evolve or Meld a card successfully.  .

Read more about the various currencies