Did we miss anything in this location? Is there something we didn't discover? Let us know!
Background
After completing the quests
Fists of Fury: Novigrad,
Fists of Fury: Skellige, and
Fists of Fury: Velen (and probably
Master of the Arena) a man will come up to you and invite you to try your luck against the Champion of Champions in Spikeroog. This conversation will trigger the quest.
Walkthrough
To participate in the fight, you'll need to talk to the bookie outside the arena in Hov on Spikeroog (#1). He'll inform you that the champion is an "errant" rock troll. When you agree to the fight, you'll automatically move into the arena.
You won't be able to use your weapons or signs during the fight, but you will be allowed to eat food and quaff potions, so the battle should be straightforward. Just engage the troll, then keep out of its reach while you heal, and then repeat. You can also quaff
Thunderbolt for extra damage, and you can put your chest armor back on for added protection.
When you defeat the troll, you'll receive the diagram for the silver sword
The Tamer, 90 crowns, and 50 xp. The troll will also tell you that its name is Athak Akydalv, but this won't lead to anything.
1 - Hov