Here is the full list of all 18 A Most Extraordinary Gnome achievements.
Save Maus from the branches he's stuck on
Die on the tutorial level
Arrive back at your home
Make the worm leave your house in anger
Make the worm trust you
Listen to the skunk speak for 5 minutes
Try to hurry through Otho's speech
Get Deerly together with her crush
Speak with the stork after finishing the story
Embrace the wall
Get back the hedgehog's lost radish friend
Beat the main three bosses
Beat the nightmare
Die from falling out of the level
Beat a boss with one life left
Beat all the bosses without losing lives
Beat each of the bosses under two minutes
Beat all of the bosses in anvil mode