Here is the full list of all 39 Planet of Mubu achievements.
Destroy the world!
Complete The Boss Zone!
Find Z!
Find M!
Complete The Maze Zone!
Find Y!
Find X!
Find W!
Find the red cube!
Find V!
Find U!
Find T!
Find S!
Find R!
Complete The Viking Zone!
Find Q!
Find P!
Complete The Run Zone!
Find O!
Find N!
Complete The Arena Zone!
Complete The Puzzle Zone!
Find L!
Find K!
Find J!
Complete The Forest Zone!
Find I!
Find H!
Find G!
Find F!
Find E!
Find D!
Find the green cube!
Find C!
Find B!
Find the blue cube!
Complete The Tutorial Zone!
Find A!
Start the game!