The Dungeon Arena is a challenge for commanders after completing the storyline in Custom Robo Arena. It is accessed by going behind the desk in the Police Station and tapping the door at the rear. In the Dungeon Arena, you can fight 100 different commanders. These are all the commanders that you had to fight in the storyline--plus a few that you haven't. In this mode, you can use both legal and parts. For every win, you can choose to continue to battle, but if you lose, you cannot. You get some money from winning, but after every ten wins, the amount of money is drastically increased. If you beat all 100 commanders, you will restart from the first commander. If you can complete the Dungeon Arena, you are indeed a strong commander.