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.
Get married.
Create a garden on your estate.
Defeat the champion of Tonstead.
Build stables on your estate.
Upgrade your main house.
Defeat the champion of Wainton.
Defeat the champion of Stonyford.
Defeat the champion of the Dunes.
Defeat the champion of Waldley.
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.