Here is the full list of all 18 My Own Little Planet achievements.
Unlocked the Nurse's info on the gallery
Unlocked the upside down thing's info on the gallery
Unlocked Willy Wheel's info on the gallery
Unlocked the Devil Boy's info on the gallery
Unlocked the Dark Boy's info on the gallery
Defeated the Abomination
Unlocked the Clown's info on the gallery
Unlocked Cheeky's info on the gallery
Unlocked Scarekid's info on the gallery
Defeated Ringleader Feddy
Unlocked The tombstone haunter's info on the gallery.
Defeated Doppelganger
Unlocked Uga-Buga's info on the gallery
Defeated Mr. Pincher
Started your very first madness
Met the boys plush bear
Unlocked Dry boy's info on the gallery
Defeated the fearsome Demon Moth