Here is the full list of all 18 Crown Champion: Legends of the Arena achievements.
Defeat the champion of Willowsfall.
Win the royal tournament.
Pass the trials.
Create a garden on your estate.
Defeat the champion of Wainton.
Defeat the champion of Tonstead.
Defeat the champion of Stonyford.
Get married.
Build stables on your estate.
Upgrade your main house.
Defeat the champion of the Dunes.
Build a bath house on your estate.
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.