Here is the full list of all 17 Thy Sword trophies - there are 4 bronze, 2 silver, 10 gold and 1 platinum.
Get all other trophies.
Finish the game.
Gain all five crystals.
Kill the Lich King & Queen.
Kill the Sorcerer of Thorn.
Chop 15 heads enemies in one game.
Kill the Lurking Horror.
Kill the Dragon Lord.
Headchop an enemy.
Find the secret gate to the loot room.
Kill the Spider Queen.
Kill a flying enemy with an arrow.
Get the key to a chest.
Get killed by an explosive barrel.
Finish the tutorial.
Hit the lantern on the title screen
Get hit by your own arrow.