Here is the full list of all 51 The Last Hex achievements.
Defeat the Lost Cultist
Defeat the Skeleton King
Defeat the Bandit Lord
Defeat The Marchosias
Defeat the Werewolf
Defeat the Vanguard
Finish the tutorial
Walk a total of 10,000 Hexes
Defeat the Demon Lord
Defeat the Butcher
Defeat the Thing From Below
Defeat the Count
Defeat the Cursed Swordmaster
Defeat The Lost as the Warrior
Defeat The Lost as the Thief
Defeat The Lost as the Wizard
Defeat The Lost as the Paladin
Defeat The Lost as the Gambler
Defeat The Lost as the Alchemist
Defeat The Lost as the Barbarian
Defeat The Lost as the Assassin
Defeat The Lost as the Elementalist
Defeat The Lost as the Champion
Defeat The Lost as the Farmer
Defeat The Lost
Die at The Lost
Die in the first battle
Defeat an enemy with set trap
Defeat the reaper
Unlock every potion
Unlock every item
Unlock every event
Unlock every enemy
Unlock every class
Have more than 30 total stats after a victory
Obtain all god items
Defeat The Lost with more than 500 max health
Complete the Cursed Church quest chain
Buy everything from 1 shop
Defeat The Lost with full health
Defeat an enemy with 1 hp left
Unlock all cards
Unlock everything
Defeat The Lost without defeating any camps
Defeat The Lost with 10,000 gold
Defeat an enemy without attacking
Defeat The Lost without attacking
Defeat 45 different enemies in a single run with Collector equipped
Lose a rare or better card to the Mimic
Have 1000 defense
Defeat The Lost within 25 minutes