Starting from rank 6 you can request cards from your friends. You can request only common and rare cards. The amount of cards you can request depends on you best league level. You can request cards every 12 hours.
Requesting Cards Edit
You can only request cards for heroes you have already discovered. To request cards, go to your Squad page and select the hero you want. Click on the Request tab on the right side of the card, and then click on the Request button. Your friends will be notified of your request and given the opportunity to fulfill any part of it up to their donate limit (or until they run out of cards for that hero).
Donating Cards Edit
When a friend donates to fulfill your request, the cards are moved from your friend's deck to your inbox, where you can collect them for your deck in the Rewards tab. In a successfully fulfilled request, cards are neither created nor destroyed. Contrast this with what happens when a player sends gifts through the Friend Shop.
Donor benefits Edit
To balance the donor's card reduction, donors are given a twofold incentive: gold coins and Experience. Per card donated, these rewards are:
Number of cards you can request/donate per request Edit
If multiple friends request cards, you can donate cards up to your limit to each one of your friends.