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