Here is the full list of all 31 Thy Sword achievements.
Finish the game with the Barbarian.
Finish the game.
Unlock the Paladin.
Headchop the other player in co-op mode.
Gain all five crystals.
Kill the Lich King & Queen.
Kill the Sorcerer of Thorn.
Get the key to a chest.
Kill the Dragon Lord.
Kill the Lurking Horror.
Get hit by your own arrow.
Kill a flying enemy with an arrow.
Unlock the Rogue.
Kill the Spider Queen.
Get killed by an explosive barrel.
Headchop an enemy.
Unlock the Viking.
Bet 100 gold and get 21.
Collect 1000 gold.
Save the witch.
Finish the game with the Valkyrie.
Finish the game with the Viking.
Finish the game with the Paladin.
Finish the game with the Rogue.
Gamble away all your money.
Chop 50 heads enemies in one game.
Find the secret gate to the loot room.
Die for the 100th time.
Finish the tutorial.
Finish the game in hero mode.