Wanted Missions (chests) are optional missions that are a great way to earn much needed in-game items. You can find your mission chests in the upper left-hand corner of your screen. 

There are three (3) different types of Wanted Missions: 

Monsters: kill 100 monsters in a province or quest
Hero: defeat 40 heroes in raids and Alliance Wars (Please note, only the heroes beaten in raids you initiate count towards your Wanted Missions)

Titan: with the help of your Alliance, slay 5 Titans

Please note, each Mission has a cool-down period before a new chest is available. But if you are patient, a Rare Wanted Mission chest may appear with the added opportunity for loot.