Arena is a special game mode, where you can compete for the title of the strongest player in Korador.
In this mode, the time of the battle is limited (5 minutes). In order to win, you need to defeat all of the enemy's heroes before time runs out. In the Arena tab, you can take part in Local or Global Arenas. Opening one of the tabs, you are offered a choice to fight with one of the three enemies presented. If the opponent is too strong, you can always change the list by tapping the Refresh button.

Pick your Arena opponent based on their rank. If you win, you get their rank, and they get yours. If you lose, your rank doesn’t change. Rewards will be sent to your in-game mailbox once every 24 hours, and their value will depend on your current rank. In the Local Arena the next battle is available in 10 minutes.In the Global Arena, you are also offered a choice to fight with one of 3 enemies. The list of opponents can also be changed by clicking on the Refresh button.
Pick your Global Arena opponent based on their rank. Don't forget to pay attention to the tags in the upper left corner. They show bonuses that are due to any races or classes for today.
If you win, you get their rank, and they get yours. If you lose, your rank doesn’t change.
Ranking rewards can only be obtained if you participate in at least one battle a day.
Rewards will be mailed to you once every 24 hours, and their value will depend on your current rank.
Every day the race changes which will be given a bonus. The bonus affects  champions in the Global Arena.