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.
Make friends with a star-spawn.
Perform the complete Ritual of Binding.
Escape the Mountains of Madness.
Free 500 trapped souls from the Asylum.
Survive for 3 minutes after Azathoth appears.
Finish the game in New Game+ mode.
Perform the Ritual of Binding.
Acquire the Soul of Cthulhu.
Acquire the Soul of Nyarlathotep.
Destroy a lizardman statue.
Read the complete History of the Library.
Acquire the Soul of Dagon.