The Scribblenauts title screen functions as a sandbox mode. There are a variety of them, unlocked by writing items of different categories.
Title Screen 1 - No Criteria[]
Your starting point in Scribblenauts.
Title Screen 2 - Write an animal[]
Bear, Deer, Camel, etc.
Title Screen 3 - Write a vehicle[]
Title Screen 4 - Write an insect[]
Title Screen 5 - Write a plant[]
Flower, Tree, Venus Fly Trap, etc.
Title Screen 6 - Write an NPC[]
Doctor, Fireman, Gamer, King, Ninja, etc.
Title Screen 7 - Write a container[]
Title Screen 8 - Write a musical instrument[]
Title Screen 9 - Write a material/element[]
Plastic, Iron, Copper, Gold, Silver, etc.
Title Screen 10 - Write a piece of furniture[]
Bed, Chair, Desk, Table, etc.
Title Screen 11 - Write something fantasy/sci-fi themed[]
Title Screen 12 - Write a building or piece of terrain[]
Title Screen 13 - Write a celestial body[]
Earth, Moon, Sun, Uranus, etc.
Title Screen 14 - Write a scientific or medical instrument[]
Calculator, Scalpel, etc.
Title Screen 15 - Toy or entertainment item[]
Write a toy or entertainment item. Computer, Internet, and TV work, as do baseball and football.