Downloading a ROM to play Scribblenauts or any other game is patently illegal. Acquiring a game through downloads not licensed by the producer of the game itself is a form of piracy, and is in clear violation against the owner of the trademark's intellectual property.
A ROM is a chip used in a video game that contains the game's software. Individuals often download ROMs so that they can play games without purchasing the cartridge or the accompanying game systems. As explained by Nintendo, this action is illegal because the information contained on a ROM is the property of the company that initially produced the game, and use of this information in any other form is a violation of important copyright laws.