Horns can be obtained from your friends or when your friends use your Hero. Horns are used for summoning units or equipment. Friends can send Horns to each other once every 24 hours. The more friends you have, the more chance to get help in a battle. Friend units will only fight for fifteen seconds from when summoned. You can only have one summon per battle. The friend that joined you in the battle will receive five Horns in their mailbox.