Chests with random reward

Chests with random reward contain mercenaries or medals. Chests can be given as a reward:
 * Iron Chest contains one of the mercenaries or medal. It's available every hour for free.
 * Chest with Medals contains five random medals for upgrade mercenaries.
 * Bronze Chest conteins either a mercenary, part of mercenary, or a medal.
 * Silver Chest contains either an uncommon mercenary, or part of a rare mercenary.
 * Gold Chest contains either a rare or epic mercenary, of their parts.
 * for everyday playing;
 * for inviting friends;
 * for completing certain missions;
 * for winning a battle on global map;
 * for winning the tournament;
 * also сhests are sold in the Shop.