Begin a new game after losing your last life. Create the Glass Key and enter the door. Follow the passageway to reach the first turn. Take and use the Vitriolok at this location.
At the Map screen hold Down B and press Select.
Hold Left A B and press Start at the map screen. A "Pass Key=" item will appear in inventory. Drop this item into a pool to change it into the next magic item in the following order. "Pass Key=" acts as any key "Downlevl" to go to the next level "Uplevel" to restart the current level and "Superpow" for invincibility.
Hold Up B and press Select at the map screen. Repeat this code to cause different items to appear.