Here is the full list of all 25 Scribblenauts Unlimited achievements. It takes around 8-10 hours to unlock all of the achievements on Windows.
Get all the Starites in any level
Bring 3 Starites to Lily and unlock the world map
Bring 8 Starites to Lily
Bring 12 Starites to Lily
Bring 16 Starites to Lily
Bring 24 Starites to Lily
Bring 30 Starites to Lily
Bring 40 Starites to Lily
Bring 50 Starites to Lily
Bring 60 Starites to Lily
Get all 106 Starites
Help all 40 of Maxwell’s brothers
Get all object Shards in the Living category
Get all object Shards in the Food category
Get all object Shards in the Vehicle category
Get all object Shards in the Music category
Get all object Shards in the Tech category
Get all object Shards in the Weapon category
Get all object Shards in the Clothes category
Get all object Shards in the Misc category
Get all 217 object Shards
Change your Avatar
Create an object using the Object Suggestor
Make a new object using the Object Editor
Download a custom object from another player