Donkey Kong

Level select:
Press Up(2), Down, Up, Down, Up(4) at the title screen.

Display level statistics:
Press Select at the title screen to display the time completed and high score for all levels on all saved games.

Hint: Jungle level 2-3: Easy completion:
There is a barrier that goes down as soon as the level starts. Use the ladder creator and put it under the barrier. If done correctly, you should be able to make it under with the key.
Information in this section was contributed by Cheats king.

Hint: Item activation:
When you activate an item, after you put it where you want it repeatedly press A and you can activate another one. Do not do this too frequently, or the game will not let you stop activating items.
Information in this section was contributed by Cjllonewolf.

Hint: Jump higher:
To jump higher, press Down + B then quickly release. You will land upside-down. Then, press B again to jump high. You can also quickly press B again after the first jump, but you have to wait for Mario to lift his hands in the air.
Information in this section was contributed by Kdogone4.

Hint: Backflip:
Run forward, then quickly press B + D-pad in the opposite direction you were originally traveling. You will do a backflip.
Information in this section was contributed by Kdogone4.