This is an odd moment for me. The most obscure game I can recall is Pokemon: The First Movie on the Game Boy but seeing as I've never played it and don't think it was worth shouting about, what about Mole Mania for the Gameboy?
Mole Mania sees you playing as a small mole that could dig holes and push things. That was sort of it...Your mole's wife has been kidnapped by an evil Farmer for some reason and it's up to you to save her! You solved a puzzle contained in a small maze to progress to the next small maze. Get it wrong and you can't get anywhere and it was easy to do. Usually, this would all revolve around lobbing a ball towards something to smash the way forwards open. These balls would fall down the holes you make while digging around and popping up from the dirt, losing them forever, adding a level of caution to your tunnelling. You also had to fight bosses with nothing but your tiny mole muscles and their abilities with chucking spherical objects around. There were some real weird ones and I believe you have to fight the sun at some point. I believe it was the stiff competition that makes this one relatively unheard of. It was up against things like the Mario Land games, the Gameboy version of Donkey Kong, The Gameboy Camera and Warioland. All of which are probably far more memorable. Although, my memory for the market at that time is rather hazy as I was probably under 10. Anyone else remember this?