To really get into the meat of Chapter 3 in Paper Mario: The Thousand-Year Door, you’re going to need a Blimp ticket. You’re told that, in order to get a blimp ticket, you need to see Don Pianta. Actually, let’s start there.
To talk to Don Pianta, you first need to meet his rival, Robbo. To get there, you need to slip through the crack next to the Trouble Center. There, you’ll have to pay 64 coins. Robbo will then tell you that, in order to see Don Pianta, you’ll need to buy a Dried Mushroom and a Dizzy Dial, then give the clerk the password “Yellow.” Well, first she’ll ask what color your mustache is. You can say yellow, but she’ll then just correct herself and ask what your favorite color is. Give her the answer “yellow,” and you’ll be let through the back door.
Up the stairs, you’ll meet with Don Pianta. He’s vaguely threatening, but eventually will give you the deal that if you can track down his daughter and former underling, he’ll give you the blimp ticket. They’re planning on eloping, and he needs to “talk” to them.
Once the conversation is over, you’ll need to head to the Docks.
These are South of Rogueport’s main square. You’ll need to go right onto the docks further south, as the couple are standing at the end of it. Talk to them.
It doesn’t matter what you tell them. You can say that you won’t rat them out to Don Pianta, or, inversely, you can tell them that you are. It doesn’t matter. Once the discussion is over, return to Don Pianta. At that point, the couple will burst in and hijack the conversation. It’s a pretty mild scene. Cute even. This is a Mario game, after all.
In any case, Don Pianta will excuse the couple through some more veiled threats. Afterward, he’ll give you the blimp ticket. You can disembark through the area north of West Rogueport.