Here is the full list of all 15 Sokocat - there are Islands achievements.
Complete level 50
Complete level 45
Complete level 40
Complete level 35
Complete level 30
Restart an island 10 times.
Complete level 25
Use bridge
Complete level 20
Complete level 15
Complete level 10
Use platform
Complete level 5
Throw a box in the water
Complete level 1