Mother (aka Earthbound outside of Japan) has a huge following even though a single game was released in North America. Nintendo of America flirted with the idea of releasing the NES game, but since the Super Nintendo was out they canned the project. Prototypes of the NES cart do exist and one popped up on eBay for the sky high price of $3499. At that price the cartridge went unsold and the sole counter offer was declined. It’s hard to say if any NES proto is worth that much money, but compared to the NES World Championship gold carts the Earthbound prototype doesn’t seem that outragous.