There are a number of Mario and Luigi RPGs, and I've enjoyed just about all of them until just about the end. Like most RPGs, the end with the Big Boss Battle Fake-Out. You reach the Sacred Destination and engage in battle with the big scary monster (or person) you've been following (or fleeing) for most of the game. As soon as you defeat that monster, another, scarier monster appears and you must fight it immediately, with your supplies now quite low.
Sometimes there is a third boss.
Yesterday, as I walked to the bus, I began the first big boss battle. Before the bus had left the city, I'd finished the battle and the second one had begun. I fought against the evil elder Shroob princess for about two hours, and hadn't finished by the time the bus got to Bethlehem. Finally, incredibly bored with the game, and disgusted by the inanity of the battle, I just shut it off and put it away. I don't think I'll try to win it again any time soon.
When I got home, I looked at a FAQ to see if I had missed any obvious trick, and I had not. I did see, though, that there would be a third boss after the second. Ha!