Here is the full list of all 15 Eldritch achievements.
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.
Finish the game in New Game+ mode.
Finish the game in under 10 minutes.
Deposit 9,999 artifacts in the bank chest.
Perform the complete Ritual of Binding.
Read the complete History of the Library.
Escape the Mountains of Madness.
Perform the Ritual of Binding.
Acquire the Soul of Cthulhu.
Acquire the Soul of Nyarlathotep.
Destroy a lizardman statue.
Acquire the Soul of Dagon.