Here is the full list of all 20 Feed All Monsters achievements.
Travel with the food bus from the Grasslands to the Snowy Mountains
Turn the music off and on 10 times in a row
Watch the credits
Solve Island 6
Unlock all photos
Solve Island 5
Unlock 35 photos
Unlock 30 photos
Solve Island 4
Unlock 25 photos
Solve Island 3
Unlock 20 photos
Walk a combined total of 1000 tiles
Unlock 15 photos
Solve Island 2
Unlock 10 photos
Solve Island 1
Unlock 5 photos
Click any character three times in a row.
Feed 100 portions of food