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