Boxing [Model DMG-BXA]

Maximum power:
Start either a new single player or a two players game. At the player's character selection screen press Up three times and Down three times in any order and finally press Select. Continue to setup your character. At the Power management screen, press Up 3 more times and then Select. If done right, the main power meter will be full and you'll be able to set up the max parameters to your character.

Extra 255 continues:
Start a new single player game. At the Finish blow select screen, hold Down + Select + Start, then press A. If done right, the limit of the continues will be increased up to 255 instead of 3, so virtually you'll have an unlimited continues.

Easter egg:
Start a new single player game. As you may notice, the Round number screen will show you the Bunny girl scrolled higher and higher up with every round. The maximum position reached at 12th round. While 12th round screen is displayed, hold Down and quickly press A or B to scroll the Bunny girl up to 24 more lines, revealing the full picture.