Here is the full list of all 25 MazM: The Phantom of the Opera achievements.
Witness the 'Phantom of the Opera' at the farewell party.
Get Carlotta's help when in a slump.
Destroy the 'masterpiece' on purpose, to infuriate someone.
Reveal the identity of the horrifying man.
Meet Meg Giry, Sorelli, and Jammes with Christine
Believe in the one you love, risking your life.
Find out the truth about the flaming head.
Force Meg with an order again.
Lie to Erik, which won't work.
Give the Mask to Erik.
Give the Mask to Melek.
Take the train ticket.
Reject the train ticket.
Acquired footnote
After meeting the Angel, find singing skills have improved.
On the first payday, face humiliation while trying to show authority.
Face Carlotta's punishment after she finds out the truth.
Find out what the kitty is thinking.