In fact, it is important to emphasize that the battle arena is only available to those who have purchased the Deluxe edition of the game. Otherwise, you won't be able to access it. So, all you have to do is move to the entrance to the Forbidden Forest. To do this, move north from Hogwarts. You will find a flying flame at the entrance to the Forbidden Forest during one of the story missions, when Sebastian or Natty will take you to Hogsmeade.
You need to find the sinister statue. Destroy several vases scattered around the area to enter the dark arts battle arena. The same arenas are in different parts of the game world.
The action game also received a content update.