Pokemon Celebi Cartridge NFR
One of Nintendo's successful campaigns to draw attention to new and upcoming Pokemon games for the Nintendo DS was to promote a downloadable character(s). I saw the success of this campaign first hard when my children was drawn to the characters GameStop offered before Pokemon Black & White came out. Of course, this isn't the first time Nintendo had done a free downloadable character. Earlier versions of Pokemon for the DS also had similar promotions.
A seller on eBay has a few of the Celebi cartridges. These NFR's would have been used at a GameStop to help promote Pokemon Black and White by letting everyone download a character Pokemon named Celebi. From February 21st through Marc 6th of this year, fans of the series was allowed to download the character if they have one of the previous Pokemon games for the DS. GameStop has few hundred of stores in the U.S. so I dont think this will be the last time we'll see this cartridge. In fact, the seller has several more listed that has a price that will sticker shock you.
Update: The seller posted under the comments of this post.