Challenge Event is a limited-time event where all participating players compete for a high score.
Challenge Events occur once a month. The goal is to play through the stages of a Tier and defeat enemies to increase your Master Score. The better your Master Score is, the better your placement is in the leaderboards.
All players who have unlocked the Quests can participate in Challenge Events. There are 3 Difficulty Tiers (Rare, Epic and Legendary), all of which have multiple stages. Each Difficulty Tier of a Challenge Event has requirements that need to be fulfilled, for example, they will limit the rarity of heroes and troops allowed in the battles. A Player can complete any or all of the Difficulty Tiers.
Completing all stages of a given Difficulty Tier will give you a one-off completion reward, which are rewarded when the Tier is completed. You can check the contents of the completion reward from the Challenge Event menu. In addition to this, at the end of a Challenge Event Participants will receive their Participation Rewards which are based on their final ranking in a given tier. The Participation Rewards can also be viewed by tapping on the Challenge Event Menu.