In-game reset:
Press Start to pause game play, then press Select to exit the current level. Note: This can only be done in levels that have been previously completed.

Hero mode:
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, and pictures.

Start/Continue a file with 50 lives
Highlight the "Erase" option on the game selection screen. Then, hold Select and press B, A, R(2), A, L. A sound will confirm correct code entry. When you start the game, you will now have 50 lives