Enter "WE5T ONE" at the Retro Password entry screen after selecting "New Game" to start as Hu-man with all hearts, full inventory, and 900k gold.Play as Wonder Girl
At the title screen, scroll up until the title of the game is highlighted. Select "Confirm" to switch between Wonder Boy and Wonder Girl.Switching characters
After completing the game or using a password to re-obtain the human form you start the game with, go to any transformation room while in Hawk-Man form and hold Up + X + B while you fall on the platform. When you transform, you will turn into the character you did not choose at the title screen (Hu-Girl if Hu-Man and vice versa). This effect will save to your file, basically acting as if you had picked that character from the beginning. The trick can be repeated whenever you want to swap back and forth between the characters.Extreme mode
When choosing a difficulty in v1.0.3c or later, hold X until you are given the option to play the game on the Extreme difficulty.Alternate Modern and Retro mode
Repeatedly press ZR to switch between Modern and Retro graphics. As the horizontal wipe effect moves back and forth, it will gradually slow down and eventually freeze in place, leaving the left of the screen in Modern mode and the right of the screen in Retro mode. How much of each side is present is dependent on the timing of the button presses and can be manipulated with practice.