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