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