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