Here is the full list of all 15 Puppies vs Undead achievements.
Complete a level higher than your level
Win 1 Fight
Collect 15 Diamonds
Spend ALL your Diamonds
Collect 50 Diamonds
Collect 100 Diamonds
Earn 1,000 Coins in a Fight
Win 10 Fights
Win 25 Fights
Win 50 Fights
Find a Gift in the game
Buy all Towers
Earn 3 Stars in 5 Levels
Earn 3 Stars in 10 Levels
Earn 3 Stars in 15 Levels