Here is the full list of all 14 The Onion Knights trophies - there are 11 bronze, 2 silver and 1 gold.
Achieve level 50.
Upgrade 20 mercenaries to 5 star grade.
Upgrade 15 skills to 10th level.
Kill 50,000 Infantry.
Kill 40,000 Armored Soldiers.
Kill 30,000 Throwers.
Kill 20,000 Chargers.
Kill 50,000 Paratroopers.
Destroy 5,000 Catapults.
Kill 100 Dragons.
Upgrade Cannon to 50 level.
Upgrade MP Storage to 50 level.
Earn 300 stars from the stage.
Earn 20,000,000 gold in extreme mode.