Here is the full list of all 14 Semblance achievements.
Change shape 200 times
Visit every level in the Snowy world
Startle 250 critters
Deform platforms 300 times
Change into each of Squish's shapes within 3 seconds
Visit every level in the Cuddly world
Visit every level in the Swamp world
Visit all the secret shrines
Visit all the wall paintings
Catapult out of a platform 100 times
Collect all Cuddly world essences
Collect all Swamp world essences
Collect all Snowy world essences
Smash all mosquitoes