After completing the "Fists of Fury: Velen", "Fists of Fury: Novigrad", and "Fists of Fury: Skellige" quests, a man will come to you and offer you a chance to fight the champion of champions.
Geralt had already won a great many victories while fistfighting opponents across the land, but still could not call himself the best of the best. The champion of champions remained undefeated, waiting for Geralt to challenge him for his title.
Go to the village of Hov on the island of Spikeroog and talk to the bookie. If you have not yet completed the "Master of the Arena" quest, the bookie will inform you that the arena is closed due to an unresolved incident and you will have to complete this quest first.
Once you get rid of Ulle, there will be nothing to stop you from facing the current champion of The Arena. This time it will be a well-developed rock troll.
During the fight you will be able to use consumables and the troll will be sensitive to your attacks from behind. After defeating the troll, you will be declared Champion of Champions and you will unlock the "Brawl Master" achievement. You will also get 90 crowns, and Diagram: The Tamer.
