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