Here is the full list of all 20 Duke of Defense achievements worth 1,000 gamerscore.
You defeated 2500 enemies!
You defeated the Fire Wizard!
You survived your first encounter with the Fire Wizard!
You unlocked 5 heads!
You defeated 500 enemies!
You are now clearly the new Duke of Defense!
You collected 50 coins in a single streak!
You equipped a head that wasn't the default!
You were wisked away to a new place!
Completed the tutorial!
Build 250 towers!
Collect 5000 coins!
Collect 25 gems!
Complete 100 waves!
Unlock 15 heads!
Unlock 30 heads!
Defeat the Ice Wizard!
Defeat the Void Wizard and fulfill your destiny!
100% complete the game!
Gather your friends and prepare for a great battle!