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.
Hints
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.
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.
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.
Backflip
Run forward, then quickly press B + D-pad in the opposite direction you were originally traveling. You will do a backflip.