Here is the full list of all 15 Eldritch achievements.
Deposit 9,999 artifacts in the bank chest.
Finish the game in under 10 minutes.
Finish the game without taking any damage.
Finish the game in New Game+ mode.
Free 500 trapped souls from the Asylum.
Escape the Mountains of Madness.
Make friends with a star-spawn.
Perform the complete Ritual of Binding.
Perform the Ritual of Binding.
Acquire the Soul of Cthulhu.
Acquire the Soul of Nyarlathotep.
Destroy a lizardman statue.
Acquire the Soul of Dagon.
Survive for 3 minutes after Azathoth appears.
Read the complete History of the Library.