Highlight the "Erase" option on the game selection screen. Then, hold Select and press B, A, R(2), A, L. If you entered the code correctly, you will hear a sound. When you start the game, you will now have 50 lives.
Successfully complete the game with a 100% rank. Start a new game and select two player mode to access the "Hero mode" option. In this mode, you play as Diddy Kong only, with a new costume. There are no Donkey Kong Barrels, Checkpoint Barrels, or pictures.
When fishing, get a combo. When you see the exclamation mark above Diddy's head, you can go somewhere and he will follow you. This will help you catch more fish and get more combos.
Pause the game, then press Select to exit the current level. Note: This can only be done in levels that have been previously completed.