Mr. Do - Extremely Rare Test Cartridge / Review Copy / Prototype (Gameboy)

A one-of-a-kind piece of video game history, can now be yours! 

We came across this stupidly rare cartridge, when cleaning out the basement of a former dealer of Intellivision, here in Denmark, and bought a huge collection from him. 
He did not know where he got it from, but he also used to review games, which is likely why he still had it. 

These cartridge were sometimes given to reviewers, and other times used to test/develop games. Reviewers were not supposed to keep them, but a few has started surfacing in recent years, becoming highly sought after collector's items. 

This is currently the only know copy of such a cartridge, with the Mr. Do! rom on it. Nobody else has found one of these yet. 

We have had a tech wizard (leader of well known video game school, Dania) help us dump the rom from this game, and unfortunately, our findings show there is no difference on this version, and the final rom - but we're not 100% sure. There could be tiny differences, we haven't been able to deduce. 

No matter what, it is a seriously cool item to have on display in any collection. 

Condition: Good. The label has some wear and tear, but it is tested and works.