Here is the full list of all 26 Metamorphosis achievements.
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Read the letter from the Tower
Wake Josef up
Gain access to The Lawyer's office
Find the Procedure
Sail the ship
Run the projector
Set Titorelli's assistant free
Become the Agent's informer
Survive the visit to the Tower
Rediscover humanity
Traverse your first wall upside down.
Make Lenni fall for you
Truly understand the Preacher
Gain access to the Bugville Underworld
Betray Josef
Ride the sandwich
Suffer the fire, water, poison, electricity, overbearing gravity and squashing
All those Effigies in ruin
Communicate to Josef his trial date
Kill the tiger
Censor the document
Meet your first bug
Feed the Hunger Artist
Obtain the certificate
Use the Roboarm