Super Mario Bros
Continue Game Play
Hold A at the Game Over screen. While keeping that button held, press Start when the title screen appears. Alternatively, hold A and press Start twice at the title screen or hold A + B and press Start at the Game Over screen.
Toad Talks to No One
When you get to any Boss except 8, small jump over the Boss stand next to the axe. When he gets close, jump on the axe and his head at the same time, as if you were trying to get fire power while small. If you land correctly, you should die but will not lose a life. The screen will show Toad saying "Sorry Mario, but our princess is in another castle" will appear, but he will be standing alone and it appears as if he is talking to himself. You will then move on to the next stage.
Pipe
In the World 8-4 castle, go through the first two pipes to continue to the third area. In the third area, go past three of the pipes, but do not jump over the lava. Stand by the edge of the lava pit, then go back to the pipe before the lava pit (third pipe). You will then be transferred to the next area (underwater).
Ongoing Level
On any level, go to where the stairs with the flagpole at the end is located. Go on top of the last stair. Then, sprint and at the very edge of the stairs, jump. If done correctly, you will have jumped over the flagpole and onto the other side. Once there, you can either jump on the pole or keep running. Note: If you keep running you will continue until time runs out and you cannot go back.