X and Z only work once you have entered a fight. As for not getting past the first screen, once a mode is selected, you have to press enter and either win or lose to reset. But that’s really odd about not being able to fight any bosses. Not sure what happened there.

The game’s ending is supposed to play when the final boss has been beaten. There is a game attribute list that keeps track of who is beaten once they are defeated. The things that transport you to the boss levels are only supposed to disappear if the name of the boss appears in the list, however this is clear by default.