Duck Tales 2 has become a rare and sought after game among NES collectors fetching around $200 for a copy. If you are one of those people who want something really rare and unusual you can always purchase a prototype.
A Duck Tales 2 NES prototype has surfaced and is up for sale on eBay. The owner of the prototype is steem69 who is a well known collector among the community. The prototype is the NTSC version of the game and uses a PCB NES-UN-ROM-01. The date on the EPROM is 12-12-92. Steem69 also posts a video showing him actually playing the game..
The current asking price is $599.