Gotham

Batman Vs. Joker is the first story misson of Scribblenauts Unmasked.

Walkthrough
The mission starts with Maxwell stumbling upon the Joker's clown car, finding the Joker as well as Doppleganger. Batman quickly arrives in his Batmobile, and tells Maxwell to deal with the items Doppleganger spawns.

Destroy the Robosaur
Doppleganger's Robosaur is destroyed, and he tries to escape with the Joker. The Joker declines, having too much fun fighting Batman. Lily insists that Doppleganger remains unharmed, as he could be useful later on. Batman, out of gadgets, requests a weapon from Maxwell.
 * Any weapon will be able to destroy the Robosaur. It's recommended to use a ranged weapon to stay out of the Robosaur's range.

Give Batman a Weapon
Surrounded by police cars, the villains have one last trick up their sleeve. Doppleganger uses his notebook to make Batman frozen, and the two teleport away.
 * Any weapon or projectile will work.

Unfreeze Batman
Commisioner Gordon enters and shows Batman a Starite his men found a block away. The group realizes that the Joker and Doppleganger are searching for Starites just like Maxwell and Lily, which would cause great catastrophe if the Starite's power fell into the villain's hands.
 * Use an item that creates fire, such as a torch or flamethrower.
 * Add an adjective such as warm.