To unlock Mario, play as Yoshi and try to unlock at least 8 stars, if some stars are difficult to earn, such as "Mario Wings To The Sky", skip them and move on to other levels. Once you get 8 stars, go to the upper-right corner and enter the door there.
All things aside, the game is still considered a classic, albeit an infamous one, and is among the rarest games on the console. Players can expect to spend aroundR$350 for a complete in box copy, and around twice that for one that's new and sealed.