Here is the full list of all 18 Crown Champion: Legends of the Arena achievements.
Get married.
Defeat the champion of Waldley.
Upgrade your main house.
Defeat the champion of Sandworth.
Build a bath house on your estate.
Defeat the champion of Greenwood.
Build a guard tower on your estate.
Defeat the champion of the Temple of Ueres.
Defeat the champion of Ada's Alehouse.
Defeat the champion of the Dunes.
Defeat the champion of Stonyford.
Defeat the champion of Wainton.
Defeat the champion of Tonstead.
Defeat the champion of Willowsfall.
Pass the trials.
Win the royal tournament.
Build stables on your estate.
Create a garden on your estate.