Challenges are weekly events that you can take part in by playing the game and completing a specific Challenge mission.
Challenges always start at the end of the week on Friday and last 66 hours. When a Challenge begins, all players are divided into groups by level and compete against each other.

To enter a Challenge, click on the purple flag with a gem in your dungeon; the flag will also show your current place in the challenge:
Note that the golden gem is always displayed on the Challenge icon and DOES NOT indicate the reward you will receive at the end.

If the Challenge has not yet started, you will see the following icon:

Click on it to see your results in the previous challenge:

Players in Challenges are divided into 5 groups by level:

Level 1-10
Level 11-20
Level 21-30
Level 31-40
Level 41+

However, a player's level will only be taken into account at the start of the Challenge when forming groups. For example, if a level 10 player reaches level 11 during the Challenge, they will remain in the first group.

Leaderboard and rewards

The reward for taking part in the Challenge depends on the level of the group. The higher the level, the greater the reward.

You can see your current ranking and reward on the Challenge screen.

While this screenshot only shows 4 possible rewards, there is actually a fifth. This is a consolation prize, which you can view by tapping the question mark icon next to the reward.

Players are ranked on the leaderboard. You can view the leaderboard by scrolling down in the Challenge window.