Here is the full list of all 12 Castle Chaos achievements.
Capture all castles in your kingdom
Defeat one or more AI players on difficulty setting "Easy".
Start a match in Castle Chaos
Kill a gnome just before he places a bush.
100 gnomes killed.
Defeat one or more AI players on difficulty setting "Medium".
Defeat one or more AI players on difficulty setting "Hard".
Defeat three AI players on the "Hard" setting.
Succeed in repairing your castle walls by controlling a gnome.
Destroy all castles of an opponent.
Defeat a team of three hard AI opponents.
Three human players team up against a hard AI opponent.