Instructions
Adventure Mode
Select "Adventure Mode" from the main menu. Set the game's difficulty to "Very Easy." Select the character you want to play as.
Fight your way through each side-scrolling stage by defeating all the enemies that attack you. Some stages have special conditions. For example, in Brinstar, platforms periodically sink below the lava. Find a safe spot before you sink, too. If you lose a life, quit the game and restart Adventure mode.
Defeat the last boss, Bowser, on the 12th stage. When you complete Adventure mode with no lives lost, Dr. Mario appears on the character roster.
Classic Mode
Select "Classic Mode" and choose "Very Easy" as the difficulty. Select Mario as your character.
Beat each mission in Classic mode. Missions include breaking all the targets, racing, participating in a team battle or defeating a giant enemy. It is acceptable to lose a life or two, but if you lose all your lives, you must use a continue to proceed. If this happens, quit and restart the game.
Beat Crazy Hand on the 11th mission. Crazy Hand floats around the arena and throws bombs or tries to squash you. When you kill it, Dr. Mario unlocks.