If you've visited Toys "R" Us for their downloadable Animal Crossing: Wild World Mario-themed items, you may have received a new, rare resident as well.
There are six monkey-species villagers in the game, but they do not appear normally. Their appearance with this promotion marks the first time they've been available legitimately in the U.S. Reports have the monkey villlagers appearing in the U.K. and Australia as well as Japan alongside similar promotions.
Even if your town is full, you are likely still able to participate. The monkey villager will move into the "ninth slot", which is used for moves between friends' towns, and wait there until there is a vacancy in your town or the town of a friend you're connecting to. One particularly enterprising player at Animal Crossing Ahead's forums started a new town with the starter four residents; accepting the promotion found a new monkey villager moving into every one of the unoccupied slots in town.
The promotion runs until the end of this week, though reports say Nintendo may permit the promotion to be extended due to problems setting up the download stations in Toys "R" Us stores.