Here is the full list of all 21 Board Defenders achievements.
Complete a level with 3 stars
Capture 10 enemies
Capture 100 enemies
Capture 500 enemies
Capture 1000 enemies
Lose two pieces at the same time
Complete 10 levels with 3 stars
Reach combo x15 with Marie the Queen
Reach combo x12 with Bob and Rob
Reach combo x11 with Paul and Paulo
Reach combo x10 with the Johnes brothers
Reach wave 8 in “Marie the Queen” challenge
Reach wave 8 in “Bob & Rob” challenge
Reach wave 8 in “Paul & Paulo” challenge
Reach wave 8 in “Johnes brothers” challenge
Complete all Forest levels
Complete all Playville levels
Complete all Magic Tree levels
Complete all Forest levels with 3 stars
Complete all Playville levels with 3 stars
Complete all Magic Tree levels with 3 stars