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