Here is the full list of all 12 Medieval Defenders trophies - there are 7 bronze, 4 silver and 1 gold.
Kill 50,000 enemies
Complete all levels with 3 stars
Build 1,000 towers
Kill 500 enemies with spells
Sell 500 towers
Earn 100,000 coins
Fully upgrade 200 towers
Manually send 100 waves of enemies
Kill 1,000 enemies
Build 50 towers
Complete level when your castle has 1 HP
Sell 30 towers