Scribblenauts Unlimited tells the story of Maxwell, who, after playing a prank on an old wizard, has to save his sister from a spell. In order to achieve this, he has to travel across the world and help people in order to obtain Starites and Starite pieces.
Unlike its predecessors, Scribblenauts Unlimited uses a level-based structure where multiple people with quests appear in the same zone. These people all have a puzzle that the player must solve, usually by using the in-game notebook, which spawns any item or person the player writes into it, just like in the previous games. Adjectives can also still be applied to objects, people and animals. One new feature are the riddles contained in the menu, which are categorized under subjects like "Food" or "Vehicles" and have the player simply guess what item the riddle is referring too.
Scribblenauts Unlimited also introduces an in-game object editor, which allows players to create their own items and share them online.