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