Achievement has been discontinued
due to the server shutdown. It's impossible to unlock this now. You can't level up characters or complete challenges.
Before you can work on this achievement, you must buy the Haakon Champion pack or one of the packs that includes him.
Challenges are found from , then . Champion challenges will mention a hero by name. Each day, there will be one new daily challenge for Haakon. There are also a small number of permanent ones. Most of the permanent ones are for using an attack for the first time.
Most daily challenges are something like "Kill/Damage X enemies with a certain attack." You may need to level Haakon up to unlock certain attacks. I recommend doing this in crossroads. You might be able to complete the challenge in a user-made world, but that can be buggy.