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