The Paper Airplane is a dangerous beta item in Animal Crossing. It is dangerous due to the fact that it can spread and shut down acres, until it eventually shuts down the entire town, thus crashing the game and possibly permanantly corrupting the game's data or forcing one to start a new town from scratch. This is why it was removed. The areas it spreads to are altered by the Glowing Yellow Box.
The Reason It Was RemovedEdit
Basically because it had a lot of bugs. It cannot be obtained without Action Replay codes or other hacks. The problem was that when you drop it, and when you leave an acre, it multiplies and overrides objects and acres in your town to yellow boxes until your town is sadly destroyed, so you have to make a new one. However, since the total shutdown may corrupt the game's Memory Card data, you would have to delete the corrupt data from the Memory Card and totally restart the game.