Here is the full list of all 11 Hollow Cocoon achievements.
See the "Human" ending.
See the "Descendant of a xenomorph" ending.
See the "Mayuhime" ending.
See the "UFO" ending.
Use chick.
Put your hand in both toilets.
Get all files.
Game over for the chickens.
Game over for Mary.
Complete the 10 yen game 50 times.
Complete game on "NIGHTMARE" difficulty.