Super Mario Land 2: 6 Golden coins

Secret courses:
Some levels have a second exit, marked with stars above it.
It completes the level and opens a secret course that you can't reach any other way.
Tree Zone: Secret Course 1 is on the opposite side of the trunk.
Space Zone: Secret Course 2 is reached after the Moon and Star courses.
Macro Zone: Secret Course 3.
Pumpkin Zone: Secret Courses 4 and 5.
Turtle Zone: Secret Course 6.

Scenic Course:
An optional auto-scrolling level lies off the path between the Tree Zone and the Macro Zone.
It unlocks nothing, but it counts as a completed level and can be replayed.

Bonus game:
Jump up and hit the bell at the goal of a level instead of entering the door to play the bonus game, which can give power-ups or extra lives.

Free Star:
Defeat 100 enemies and a Star (invincibility) will drop.
While invincible, defeating five enemies gives you an extra life, and every enemy after that gives another one.

50 coins at once:
Moneybags in some ? Blocks are worth 50 coins.

Level counter:
Every level you complete for the first time, including the secret courses, adds 1 point. The maximum is 31.
The game is not saved after the final level, so the full 31 can't be kept on the save file.

Hidden music:
Wait two and a half minutes on the Game Over screen to hear a hidden tune ("Totakeke's theme").

Game Over warning:
A Game Over takes away all the Golden Coins you have collected, and you must get them again.

Pipe glitch (only ROM versions v1.0 and v1.1):
Press Start and Select together as you leave or re-enter a pipe level and Mario can move through the floor.