Here is the full list of all 15 Master Key achievements.
Whack.
Boo.
Crash.
And make it double.
Congratulations!
Splash.
You found all the discs.
You found all of the cristals.
You reached the maximum of HP.
A big sword made by little guys.
You proved your worth in a battle to the death.
You solved all of the nonograms
Makes you all dizzy.
You reached the city.
Many times.