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