Here is the full list of all 16 The Misadventure Of Melon achievements.
Get your first hat by defeating the penguins!
Defeat the first boss
Complete all levels
Complete the game on hard mode
Collect all the hats in the game
Find your first golden melon piece
Find all six golden melon pieces
Buy all the upgrades
Get 3,333 coins
Complete any level in under 100 seconds
Finish a bonus level without dying