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