Inside Bowser's castle, Mario is hanging on to the end of a bridge that is about to fall into bubbling lava. His grip is slipping. Mario loses his grip and...

Well, before that happens, let's look at how he got into this situation.

Mario is inside his house, as his castle has been stolen once again by Wario.  He is about to go and take back his castle, when Toad barges in. He tells Mario that Peach has been kidnapped by Bowser again. Mario promptly sets off for Bowser's castle. He gets there a few seconds before Bowser comes flying past in his Koopa Clown Copter with Peach.

Peach: Mario!

Bowser: Bwa ha ha! Just try to save her, Mario.

Peach: Help me, Mario!

Mario: I'll-a save you, Peach!

Bowser lands inside his castle, in the central tower, which is the highest tower. Mario runs into the castle.

Meanwhile elsewhere...

It is the Dry, Dry Desert. Rushing past is a Koopa on a Wiggler. The Koopa is dressed in clothes of the Old West. He digs his spurs into the Wiggler, which turns red with rage and thunders by even faster.

Koopa: Ha ha ha!

The Koopa pulls out a bomb-like device and tosses it at the ground. It opens up and creates a portal-thing. He turns the Wiggler and thunders into the portal.

Back with Mario...

Mario runs into the castle. He runs all the way to the first red door, which is guarded by 2 Flying Hammer Bros.

FHB 1: Well, if it isn't Mario! He have been instructed to keep you out at all costs. We will not fail.

FHB 2: Right!

FBH 1: Now, Mario... Prepare to face your doom!

However, while they were talking, Mario went through the door.

FBH 1: See what you did again?!

FBH 2: Sorry, sir. I won't do it again.

Mario is in another hallway. He continues on through the castle, and runs into the courtyard. In the courtyard is a Mecha Bowser, about 3 times as big as Mario, made of metal. Driving it are the Ninjakoopas.

R. Ninjakoopa: Mario! You are just in time to be destroyed by Bowser??? 2.0!

Y. Ninjakoopa: I thought we agreed it would be called Yellow Tornado?

G. Ninjakoopa: No, it was supposed to be Green Fury.

B. Ninjakoopa: You're both wrong. It was supposed to be called Black Death.

While they are arguing, Mario gets past and enters the tower. That was much too easy... Anyway, back with the Koopa cowboy...

The Koopa is now alongside the train that heads from Mt. Rugged to Toad Town. Aha. So that's what the portal was for. He thunders into Toad Town, through Toad Town, past Toad Town, to Bowser's castle.

Back with Mario...

Mario is running up the tower while lava is rising. He gets up to a large room with a bridge across it. The lava stops rising a bit below the bridge. Mario runs across the bridge, but suddenly arrows are being shot at Mario!

Bowyer: Nyah! Not survive, you will! Orders from Bowser I have; orders to kill you! Nyah!

4 more arrows are fired, and they all miss Mario... but hit the bridge, causing it to collapse. Mario runs across it, and manages to grab the ledge. His grip starts slipping. He's sure to fall. He loses his grip and...

Suddenly, a portal opens up and the Koopa on the Wiggler comes out and saves Mario from death by lava, by jumping across the gap and grabbing Mario's hand.  He pulls him onto the Wiggler, and thunders up the remaining stairs, to the top of the tower. Bowser is at the top, and quite surprised.

Bowser: Who are you?

Koopa: My name is not important. What is, is my payment.

He turns to Mario.

Koopa: I just saved your life. I could end it right now. I will not if you give me due payment.

Mario: I have nothing to pay you.

Koopa: Hmm... Well, you are rescuing that princess over there, right? She is rich, is she not? I will accept payment from her. I will be waiting.

Saying that, he jumps off the tower on the enraged Wiggler, and through a portal.

Bowser: ... That was weird. Whatever. You will NOT rescue Peach, Mario!

Saying so, Bowser jumps at Mario, but Mario dodges, and Bowser crashes through the tower into the lava, ending his life. Mario rescues Peach, returns to her castle, and pays the Koopa, who tells them to call him "Lone Rider" if they ever meet him again. Everyone lives peacefully until 2 days later when Bowser kidnaps Peach again.