Mario approaches the shining light. Once near, he grabs the object, and it instantly stops glowing. Mario looks at the object in his hand and notices its color is red and it is shaped like a heart, but it is made of crystal, like a Crystal Star. He turns to the others and shows them the object.
Mallow: What is it?
Luigi: Mario, it kinda looks like it's made of the same material a Crystal Star is made of.
Mario: You're right, Luigi. We should show this to E. Gadd. He might know.
Luigi: There's just one problem. E. Gadd lives at the edge of Boo Woods. We'd have to pass through Toad Town to get there, and who knows what King Boo did to Toad Town?
Bowser: Hehe, I saw the whole thing when I tried to kidnap the princess. Every house was shaped like a Boo. And the Castle was turned into a bigger version of his mansion except it was Peach's Castle inside, only more King Boo's style.
Bowser: Oh, but there is one way.
Luigi: How? Your Clown Copter? It's too small for all of us to fit!
Bowser: NO! My Koopa Cruiser. I just have to call Kamek, and he'll have it right over.
Bowser pulls out a cell phone shaped like his shell, and begins to call Bowser's Keep. But from behind them, a Boo appears.
Boo: I don't believe it. They're still alive. I have to report this to King Boo.
The Boo disappears and Luigi turns around.
Luigi: ... Hey Mallow. Did you hear something?
Luigi shrugs and just thinks it was his imagination. Bowser gets off the phone and turns to the others.
Bowser: Okay, Kamek said he'll have the cruiser over the volcano soon. We just have to climb up and wait. It's a good thing I had my phone with me.
Mallow: And from the sound of it, your Keep is Boo free.
Bowser: ... Yeah. You're right!
Mario: But if your Keep’s okay, then why are you still helping us?
Bowser: ... Uh... I want the princess back to her old self.
Back in the Mushboo Kingdom, the Boo that was in Barrel Volcano has just arrived back to King Boo's Castle. He appears in the throne room to find him and Princess Boo discussing new laws.
Princess Boo: How about a day where all the ghosts go on a scaring rampage?
King Boo: Hmmm... nah. We do that already.
Boo: King Boo! Big news!
King Boo: Yes?
Boo: We got big trouble! The Mario Bros. and Bowser have survived!
King Boo: ! WHAT?!
Boo: Yeah, I saw them with my own eyes!
King Boo: GRRRRRRRRRRR... Wait. When did I give you permission to... No! It's actually a good thing you went to spy on them. What were they doing?
Boo: They were calling some Magikoopa to bring them some cruiser to take them to E. Gadd's place. But that's not all, I saw Mario holding... A CRYSTAL HEART!
King Boo: ... Did you say... Crystal Heart?
Boo: Yes sir.
King Boo: ... Okay, here's what were going to do. First, we are going to intercept that connection to E. Gadd's from Barrel Volcano. Then, once we know they are done, I need the Booario Bros to contact Star Heaven and find out the location of the Crystal Hearts!
King Boo looks at Princess Boo, who is looking around the room. King Boo then moves closer and whispers in the Boo's ear, if he has one.
King Boo: (whispering) The Crystal Hearts are the only thing that will turn Peach back into... well... her old human self!
King Boo: Now, go and get the Boo general and tell him the plan!
Boo: Yes sir!
The Boo rushes out and King Boo laughs evilly.
Princess Boo: What's going on?
King Boo: Oh, nothing dear. It's just that the Mario Bros. are still alive. So we are going to make sure that they stay exterminated for good this time.
Princess Boo: Oh... okay.
Back at Barrel Volcano, Mario and Co. have just used the spring at the end of the volcano to jump out. They are now seen sitting around the mouth of the volcano. Then, from the distance, Bowser sees an oncoming object. The others can't make it out, but eventually, they realize it's the Koopa Cruiser. It reaches them and they hop on.
Kamek: So, King Boo took over the Mushroom Kingdom and turned Peach into a Boo?
Kamek: And you need to be taken to E. Gadd's so he can identify that object Mario is holding?
Kamek: ... Okay. Let's roll!
The Koopatrol starts flying toward Boo Woods. Then, the sirens start beeping.
Koopatrol: Lord Bowser, there is an oncoming object flying straight at us!
Bowser: Put it on screen!
The screen pulls down and a flying box appears on the screen.
Mallow: It's... a box?
Bowser: Since when do boxes fly?!
???????: Ever since Prof. Boo invented it for me!
Everyone looks around and wonders who said that. The screen then changes to a Boo with red eyes. He is wearing a jester's hat and holding a jester stick.
Mario: Who is that?
???????: I am known as Booster, King Boo's one and only general!
Luigi: So... you're the one flying the box?
Booster: No, a Boo solder is flying it. But King Boo has ordered me to stop you from getting to E. Gadd's lab!
Mallow: Well how are you going to stop us?
Mario: (looking out the window) Uh, I think like that.
Mallow looks and sees that the box opens and a robotic Boo on a spring with long arms and claws for hands pops out.
Mallow: Uh oh.
Booster: Hehehehehehehe! Meet my ship-tank... BOO IN THE BOX!
Bowser: ... Dude, you kinda killed the mood there.
Luigi: Yeah, if you had a more threatening name, it would be much more evil.
Booster: GRRRRRRRRRRRRR! Quiet! I named it and I'm proud! Now, like I said before, King Boo ordered me to stop you from getting to E. Gadd’s!
Mario: But... how did he find out?
Booster: Let's just say, we sent a spy to find out if you were still alive. Now... PERISH!
BOSS BATTLE: Boo in the Box
Bowser: ARM THE CANNONS!
Koopatrol: Right, sir!
Bowser: Mario, Green ‘Stache, Puff Ball! We’re going outside!
Bowser: To destroy any projectiles the cannons missed. Kamek! You're in charge.
Kamek: Yes sir.
Mario and Co. jump out and see the Boo in the Box forming fireballs. He starts throwing them at the Koopa Cruiser. Out on the sides, Bullet Bills are fired from the cruiser and hit the fireballs. From inside the box, Booster gets angry and pushes a button. The Boo in the Box opens its mouth and fires a laser. Bullet Bills are fired again, but only a few hit the lasers, so the remaining lasers head straight for the cruiser. Mallow jumps in and uses his sonic symbols, sending a shockwave toward the lasers and destroying them. Mario looks behind him and sees a rotating cannon.
Mario: Bowser, what's that?
Bowser looks and smiles.
Bowser: Ludwig just installed it. It's the Bullet Blaster 2000. It fires Bullet Bills faster, and with the extra speed, they have more power. Go and take control. Green ‘Stache, Puff Ball, and I will defend the cruiser. You take care of that robot.
Mario nods and rushes over to the cannon. He aims and fires three Bullet Bills, and they DO go faster than ordinary Bullet Bills. The Bullet Bills hit Boo in the Box. From inside, Booster looks at the energy level, which is below half. Booster gets fire in his eyes.
Booster: OKAY! You want to play like that? Well try THIS on for size!
Booster pushes a button, and one of Boo in the Box's hands opens and out comes a long metal jester stick.
Bowser: Oh boy.
Boo in the Box swings the stick and fires a ball of magic. From the control room, Kamek looks and orders the Koopatrols to curve to the left. The cruiser manages to avoid the blast, barely. Mario fires more Bullet Bills, but Boo in the Box twirls his jester stick and forms a force field. The Bills explode without hurting Boo in the Box. Then Boo in the Box's free hand extends out and grabs the cruiser and pulls it toward him. When in range, Boo in the Box starts to form a magic beam. Mario then takes the free opportunity to fire Bullet Bills at the spring arm. They hit the arm and it breaks, giving the cruiser a chance to fly away. Mario then fires Bullet Bills, Mallow performs Star Rain, and the cruiser fires Bullet Bills as well. Bullet Bills and shooting stars pelt Boo in the Box. Inside, a siren goes off and everyone starts panicking. All the Boos fly through the walls and head back to the Mushboo Kingdom. Booster stays behind.
Booster: NOOOOOOOOO! THIS CAN'T BE HAPPENING!
Boo in the Box explodes and Booster is sent flying toward the Koopa Cruiser. He lands on the windshield. Mario and Co. head back down into the control room and see Booster. He waves nervously.
Bowser: Guys, show him the Koopa Claw.
Koopatrol: Yes sir.
A Koopatrol pushes a button and from the cruiser’s mouth, a claw appears. The claws bends toward Booster, grabs him, and flings him far away. From inside, everyone cheers.
Luigi: WE DID IT!
Mallow: ALL RIGHT!
Bowser: THE KOOPA CRUISER SURVIVES!
Kamek: Well, now that that's done and over with, shall we head to E. Gadd’s?
Bowser: To Boo Woods!
The Koopa Cruiser
flies off toward Boo Woods.
Back at the Mushboo Kingdom Castle, King Boo is seen with Princess Boo, waiting for the results of the sneak attack on Mario and Co. Then all the Boos controlling Boo in the Box rush in.
King Boo: So... how did it go?
Boo: We were DESTROYED!
King Boo: ... HOW?!
Boo: Mario, his bro, some puffball, and Bowser managed to escape Booster's final attack, and they then destroyed Boo in the Box and sent Booster flying somewhere!
King Boo turns around and grumbles.
King Boo: Hmmm, the sneak attack wasn't enough.
Princess Boo: What should we do now?
King Boo: ... Bring Booario and Booigi.
The Boo disappears and are back in a split second with Booario and Booigi.
Booario: You called?
King Boo: Yes, the sneak attack failed to work. So, I need you two to do something for me.
Booigi: Like what?
King Boo: Something like this...
He motions them closer, then whispers his plan. The Boo Bros laugh evilly.
King Boo: Understood?
Boo Bros: Yes sir!
They disappear and King Boo turns to Princess Boo and smiles.
King Boo: Don't worry, my dear, we have everything under control.
The Koopa Cruiser is seen landing in front of E. Gadd's shack at the end of Boo Woods. Mario, Luigi, Mallow, and Bowser head inside. Inside, they see E. Gadd working with chemicals. He turns to them and smiles, but is somewhat surprised to see Bowser.
E. Gadd: Ah, the Mario Bros, along with Mallow, and Bowser? Anyway, what can I do for you?
Mario: We need your help identifying this.
Mario pulls out the red heart. E. Gadd jumps back.
E. Gadd: YOWZER! That's one of the eight Crystal Hearts!
Mallow: Crystal Hearts?
E. Gadd: Yes. Where did you get it?
Luigi: We got it after battling the Czar Dragon in Barrel Volcano.
E. Gadd: ... You just acquired that Heart from one of the eight guardians.
Bowser: Eight guardians?
E. Gadd: Yes. There are eight guardians that protect these precious crystals. Czar Dragon was one of them.
Mario: Do you know any more?
E. Gadd: Sadly, I do not. But, I do know someone who does.
E. Gadd: The Star Spirits.
Mallow: -_- Yeah, didn't see that coming.
E. Gadd: Just take it to them, and they will explain everything.
Mario: Thanks, E. Gadd.
They head back to the cruiser and Bowser commands the cruiser to Star Heaven.
Up in Star Heaven, Mario and Luigi are seen walking up the path to the Star Sanctuary, where they meet with Eldstar and all the other Star Spirits.
Eldstar: Mario? Luigi? What are you doing up here?
Mario: We came to find out the locations of the Crystal Hearts.
Luigi: We need them to stop King Boo. He has taken over the Mushroom Kingdom and turned Peach into a Boo.
Eldstar: Very well.
Eldstar spins and lets off a magic dust. Then a Crystal Ball appears.
Eldstar: This Crystal Ball will give you the location of every Crystal Heart location. May we wish you luck on your journey.
The Mario Bros. turn and leave. When they reach the outside, they laugh.
Mario: Wehehehehehehehe! Too easy.
Luigi: Yeah, let’s get this back to King Boo!