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