Pinkie: Operation Friendship Rescue has begun! Let's save Dashie!

Pinkie ran ahead.

Mario: Uh, Pinkie, maybe you should let me and Luigi do the leading. We know Bowser's castle like the backs of our hands!

Pinkie: Aww...I wanna do the leading. 😔

Luigi: Isn't she cute?

Mario: ...What're you talking about, bro?  Y'know what? I don't even wanna know.

Mario and Luigi led the girls through a pipe.

Rarity: Are you sure it's safe to go down a sewage pipe? All that sewage could ruin my complexion!

Mario: Sure, I do it all the time!

Pinkie: Ooh! This'll be fun!

They all went down the pipe.

https://youtu.be/eRLunbTj3-g

Twilight: Where are we?

Mario: Underground.

Fluttershy: Is it safe to be down here? We could run out of air!

Mario: Relax, there's always a cool breeze down here, we'll be fine.

Sunset: If Rainbow Dash were down here, she'd love it.

Pinkie: What's down here?

Pinkie went down another pipe.

Sunset: Uh, Pinkie? What're you doing?

Pinkie Pie immediately squeezed out of the pipe, realizing there was a Piranha Plant inside it.

Pinkie: AAAHHH!!!! It's a meat-eating plant! HEEEEEELLLLLPPPP!!!!!

Mario: Relax, there just Piranha Plants.

Pinkie: That's even worse!

Mario: It's nothing we can't handle. Right, bro?

Luigi dozed off in a daydream.

Mario: Luigi!

Luigi: Huh? Sorry, bro.

Mario bashed a block and out came a Fire Flower.

Twilight: What's that?

Mario: You'll see!

Mario touched the flower and became Fire Mario.

All: Whoa!

Fluttershy: How'd you do that?

Mario: I'll explain later. Let's find a way out of here.

Mario and Luigi guided everyone underground, ridding enemies and finding coins.