I would have to say Monster Party. That was one of my most favorite games for the NES. A very strange, surreal, and bizarre journey of a game. Looking at various screenshots I've seen online scanned from old Japanese gaming magazines of the original unreleased (sadly) Japanese version of Monster Party (Called "Parody World: Monster Party"), it looked even more strange than the version we got. A sequel to that game, in any form, would definitely make me happy.