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