Here is the full list of all 42 Lies of P achievements. It takes around 60-80 hours to unlock all of the achievements on Windows.
Tell a lie in front of Hotel Krat Entrance.
Kill the Parade Master.
Repair a Stargazer.
Deliver a successful Fatal Attack.
[Real boy: They all lived happily ever after] Reach the ending.
[Free from the puppet string] Reach the ending.
[Rise of P] Reach the ending.
Kill the Nameless Puppet.
Strengthen a normal weapon to its max level.
Strengthen a special weapon to its max level.
Modify a Legion Arm to its max level.
Activate P-Organ to Phase 5.
Play a perfect tune on the piano at Hotel Krat.
Collect all Legion Arms.
Collect all special weapons.
Collect all normal weapons.
Collect and play all records.
Learn all gestures.
Decipher all cryptic vessels and claim the rewards.
Discover all Trinity Sanctums.
Try to assemble a weapon.
Destroy an enemy’s weapon with a perfect guard.
Kill a Stalker.
Kill the Scrapped Watchman.
Kill King’s Flame, Fuoco.
Kill the Fallen Archbishop Andreus.
Kill the Eldest of the Black Rabbit Brotherhood.
Kill Romeo, King of Puppets.
Kill Champion Victor.
Kill the Puppet-Devouring Green Monster.
Kill the Corrupted Parade Master.
Kill the Black Rabbit Brotherhood.
Kill Laxasia the Complete.
Kill the Awakened God Simon Manus.
Harvest Gold Coin Fruit.
Kill all types of Dimensional Butterflies.
Find out about the last story of Venigni.
Find out about the last story of Antonia.
Find out about the last story of Simon Manus.
Find out about the last story of Geppetto.
Find out about the last story of Eugénie.
Find out about the last story of Sophia.