Here is the full list of all 35 Lovecraft's Untold Stories achievements.
Defeat Cthulhu
Complete the story of the Professor
Unlock the Witch
Find a secret room without the Detective
Defeat Dagon
Complete any Great Old One location without having 100% information about it
Eat 100 chocolate bars
Complete the story of the Detective
Complete the story of one playable character on HARD difficulty
Get 5 curses of the Great Old Ones at the same time
Make 1 playable character go crazy, at least once
Spend 100,000 dollars and 100,000 information in the magazines
Unlock the Professor
Die in a strange place
Complete the story of the Thief
Complete the story of the Witch
Complete the story of the Ghoul
Unlock the Thief
Unlock the Ghoul
Defeat Shub-Niggurath
Defeat Nyarlathotep
Make every playable character go crazy, at least once
Collect 100% of the information of one of the Great Old Ones
Collect 100% of the information of all the Great Old Ones
Find things not from this world
See what was impossible to see
Find 75% of the mini-events
Defeat Azathoth
Complete all the side quests
Find every mini-event
Complete the stories of every playable character on HARD difficulty
Complete the story of any playable character without using the shops, and expelling them if you see one
Save the Earth from the Great Old Ones
Complete the story of any playable character without receiving any curse
Defeat every Great Old One with the same character