Here is the full list of all 49 MMY: Otherworld Mystery achievements.
Complete level 50.
Complete level 48.
Complete level 47.
Complete level 46.
Complete level 45.
Complete level 44.
Complete level 43.
Complete level 42.
Complete level 41.
Complete level 40.
Complete level 39.
Complete level 38.
Complete level 37.
Complete level 36.
Complete level 35.
Complete level 34.
Complete level 33.
Complete level 32.
Complete level 31.
Complete level 30.
Complete level 29.
Complete level 28.
Complete level 27.
Complete level 26.
Complete level 25.
Complete level 24.
Complete level 23.
Complete level 22.
Complete level 21.
Complete level 20.
Complete level 19.
Complete level 18.
Complete level 17.
Complete level 16.
Complete level 15.
Complete level 14.
Complete level 13.
Complete level 12.
Complete level 11.
Complete level 10.
Complete level 9.
Complete level 8.
Complete level 7.
Complete level 6.
Complete level 5.
Complete level 4.
Complete level 3.
Complete level 2.
Complete level 1.