Here is the full list of all 19 Gravity Ghost achievements.
Reach max hair length
Beat the game
Collect all 7 geoms
Reunite all 14 animals
Collect all 94 stars
Reunite all animals, collect all geoms, collect all stars
Float for 10 minutes without touching the ground
Make 10 earth planets
Make 10 ice planets
Make 10 fire planets
Make 10 gem planets
Make 10 water planets
Make 10 air planets
Terraform 100 planets
Carry all 14 animal spirits at once
Carry all 7 planet pieces at once
Carry all animal spirits and planet pieces at once
Terraform the biggest planet in the game
Speedrun the game in less than 50 minutes