Here is the full list of all 40 The Vagrant achievements. It takes around 20-25 hours to unlock all of the achievements on Windows.
Failed to defeat Santiago
Slay 666 monsters
Acquire a weapon or armour with 4 runestones
Defeat Headless horseman
Slay the chicken
Achieve 100 combos
Defeat Kumasith
Defeat Maximillian II
Defeat HMWV
Acquire a max ranked weapon or armour
Defeat Esgonian general
Fight Soulreaper
Keep drinking potions
Acquire an onion from the chef in Brocley village
Defeat Soulreaper
Failed to defeat Kumasith
Defeat Santiago
Stop Soulreaper
Failed to stop Soulreaper
Defeat Ground shaker
Defeat Shroom prime
Failed to defeat Shroom prime
Defeat Fallen Kumasith
Defeat Valerie
Achieve normal ending
Achieve true ending
Collect 1000000 gold
Collect 1000000 mana
Explore all areas
Acquire all skills
Acquire all recipes
Unlock all entries in Monsterpedia
Acquire Sword of verum
Unlock all abilities
Consumed 100 potions in total
Clear the game in Hard difficulty
Achieve 500 combos
Achieve 999 combos
Unlock all entries in Note
Unlock all achievements