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