Mario and Luigi come out of the lighthouse which leads to Gelato Beach.
Blue: You guys, it's terrible! Princess Peach has been kidnapped!
Luigi: Oh no! Who took her?
Blue: That guy that looks like Mario!
Mario: Which way did he go?
Blue: Well, I was waiting here when I heard a scream from Peach coming from the Pianta statue. When I got there, that imposter was running off with her. We followed them to the west end of town and we saw this Bowser submarine in the water. Toadsworth told me to return to the lighthouse to tell you guys about it when you returned!
Luigi: Thanks!
The Marios run off through the plaza and make their way to the docks where they see Shadow Mario forcing Peach into a hatch on the sub.
Peach: Mario! Luigi!
Shadow Mario jumps in and drives off to a small island.
FLUDD: That is Pinna Island. The perpetrator must be there.
Mario and Luigi watch as the Bowser Sub drives off into the distance.
Toadsworth: Oh no! You must rescue the Princess, or I'll scream!
Yellow: Please save her!
Luigi: But, how do we get there? I'm not interesting in swimming.
Mario: Hey, Luigi! Let's jump in this cannon and see where it takes us!
Luigi: Okay, Mario!
They jump into the cannon.
Pianta: Hey, get outta there!
They blast off towards the island.
Pianta: At least they listened.
They land on the beach of the island, and see the entrance to Pinna Park.
Luigi: Ooh, an amusement park! Let's go check it out!
Mario: We're here to rescue Peach, not go on rides!
Luigi: I like rides, but not the roller coaster. It's scary!
They run to the entrance and see Shadow Mario there. He runs off.
Mario: After him!
The Marios spray Shadow Mario, but Shadow Mario just keeps on running off and heads towards the fountain. He jumps into the center of the fountain, and it opens up. A giant, mechanical Bowser rises out.
Luigi: Is it just me, or has Bowser put on weight?
Mario: Now what are we gonna do?
A brown Noki walks up to them.
Noki: This looks so heroic! You two standing up against that big machine! Here, I'll let you use a special vehicle to help fight him!
Luigi: Do we have to?
Noki: Yes.
The Marios follow the Noki around the fountain and up a path. They board a pod that travels along a rail over the park. They jump in and drive off.
Mario: How's this thing gonna help us stop that Bowser robot?
They pass by two rockets and the FLUDDs pick them up and place them in their nozzles.
Luigi: We can just use th-
Just then, they go zooming downwards and through some loop-the-loops.
Luigi: I HATE ROLLER COASTERS! THEY MAKE ME SICK!
They approach the Mecha Bowser, and each fire a rocket at it.
Mario: I think it's working! We just need to get more rockets!
Luigi: And I need some Pepto Bismal!
FLUDD: Mario. There's Bullet Bills behind you.
Mario turns around and sprays the Bullet Bills and they explode. Luigi gets hit by a Bullet Bill.
Luigi: Hey, you were supposed to warn me!
FLUDD2: Sorry, Luigi.
Luigi: Hey, there's some more rockets!
The FLUDDs equip themselves with the rockets. Mario hits the Mecha Bowser.
FLUDD2: Luigi, douse they flames with some water.
Luigi: What flames?
Mecha Bowser blasts Luigi with flames, but Mario douses them.
Luigi: That hurt!
Luigi shoots his rocket at Mecha Bowser, which falls apart. The Marios jump out of the pod and walk up to it. A hatch opens up and Shadow Mario appears with Peach. Shadow Mario pulls off a bandana with a mustache painted on it and he transforms into Junior.
Junior: Leave my Mama alone you bad men! I won't let you take Mama Peach away!
Peach: Mama? I'm your Mama? You're Bowser's son?
Luigi: Bowser's son? We've seen Bowser's kids before, and they don't look like you!
Peach: But why did you pretend to be a Mario Brother?
Junior: Hey, all I know is that Dad said, "The Mario Bros. are bullies! They never fight fair!" So Papa told me to try and get them sent to prison! But now it looks like that plan didn't work!
Mario: So, now what are you gonna do?
Junior: The one thing I'm good at, escaping!
The hatch closes up.
Peach: Mario! Luigi!
The remains of the Mecha Bowser extends a propellor from underneath. A balloon pops out of the top and takes off.
FLUDD: It appears to be heading towards Corona Mountain.
Luigi: Great, now what do we do?
Mario: Hey, there's a Shine in the fountain!
Mario runs up to it and grabs it and does the Shine Dance.
Mario: Yahoo!
Luigi: Noooo! I wanted it!
Noki: Hey, I'm gonna set up a game where you get to ride the roller coaster again!
Luigi: Noooo!