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