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