Instructions
Start a "Dragon Adventure" single-player story campaign by clicking on that button on the main menu. This will take you through the stories that unfold in the DBZ universe.
Continue through the storyline until you face Zarbon during the Frieza Saga chapter.
Defeat Zarbon to unlock the normal-handsome Zarbon form. This occurs in the battle labeled "Vegeta and Zarbon." This must be done first so that you can use the regular Zarbon Green Potaras piece for Z-item fusion.
Continue to the next fight, which is labeled "Vegeta Attacks."
Save your game by clicking on the "Save" button on the menu displayed after the battle is over and exit to the main menu.
Enter the "Item Shop" by clicking that button on the main menu.
Scroll down until you see the Z Item Fusion item and purchase it by clicking on it and confirming the selection with the shopkeeper.
Exit the shop menu by clicking "Exit."
Enter your "Item Inventory" by clicking that button on the main menu.
Scroll down and select your Z Item Fusion item from your inventory. It will ask you which items you want to fuse.
Select both the Zarbon and Unsealed Potaras and confirm on the menu by selecting "Yes." These two items will fuse and you will create the "Post-Transformation Zarbon" Potaras or monster Zarbon as he is often referred to in this form. This version will now be selectable for versus battles.