Mario, Luigi, Mallow, Geno, Kamek, Jr, and the troops are seen sitting outside, waiting for Booser and Yang's return. To recap, Yang is a Duplighost with many ninja skills who is currently looking for his sister but has had no luck. So, he decided to help out Mario and Co. by looking for Crystal Hearts.
A Boo Guy had asked Mario to meet him at Club Boo in the Mushboo Kingdom. But Mario was afraid of getting caught, so Booser and Yang offered to go. Mario accepted and both ghosts infiltrated Boo Town and found Club Boo. The Boo Guy told them he was looking over Mario and Luigi to make sure they were powerful enough to take down a powerful enemy.
Then, a Boo waiter had found out that Booser was in the club and warned DJ Boo. DJ Boo took matters into his own hands and prepared his bot to finish off Booser, Yang, and the Boo Guy himself.
Mario: They should've been-a back by now.
Luigi: Don't-a worry, if something happens, Booser can handle it. And, with Yang by his side, they are a perfect team.
Kamek: I hope so.
BOSS BATTLE: DJ Boo
DJ Boo: Okay guys... get a load of THIS!
He pushes a button and a robotic claw reaches to where DJ Boo is and grabs a disc. The claw throws it at lightning fast speed at Booser. Booser acts fast and turns invisible.
Booser: That all you got?
DJ Boo: Nope! I'm just warming up!
Booser: So was I!
Booser charges toward him, floats up high, and fires flame breath. DJ Boo commands the robot to jump, which it does. But Yang appears from smoke in front of him and throws a shuriken at the bot. The bot starts letting off static.
DJ Boo: I don't think so!
He pulls a lever and one claw grabs the shuriken and throws it back at Yang, which explodes on him. He is sent to the ground, and Booser goes to his aid.
Booser: What kind of shuriken was that?
Yang: That was a bomb shuriken. I thought I could end this quick by making him blow, but it didn't go off in time.
Boo Guy: I'll handle this.
The Boo Guy reaches for his sword sash and pulls out his sword (which, if you remember, looks exactly like Meta Knight's except the red gem is replaced with a white gem). He charges toward the bot, floats up high, and slashes the air. The slash heads for the bot, which is hit, getting pushed back a little. The Boo Guy comes back down.
Booser: What was that?
Boo Guy: The air slash technique, a simple attack that all Sword Guys know.
(Note: By Sword Guys, I mean a type of Shy Guy that uses swords.)
DJ Boo: I'm not finished yet!
DJ Boo grabs a disk and starts playing it. Techno music starts playing and soundwaves head toward the Boo Guy. He covers his ears, if he has any, and drops his sword. Then, his chest begins to give off static.
DJ Boo: What the?
Then a small disc appears on his chest. It then falls off. Then, the Boo Guy begins to transform. In the Boo Guy's place is a white Shy Guy.
Shy Guy: No! My disguise.
The bot walks toward the little disk and picks it up. DJ Boo observes it.
DJ Boo: A camouflage disk. I knew something was weird when you joined. And that is that you’re a Shy Guy!
Yang begins to stare at the Shy Guy.
Yang: I have the strangest feeling I've seen him somewhere before.
Shy Guy: Okay, you blew my cover! So what? I'm still strong enough to defeat you!
The Shy Guy grabs his sword and rushes up to the bot. He jumps and spins his sword.
Shy Guy: Shy Guy technique number one... PARALYSIS!
The bot tries to move, but can't. The Shy Guy has paralyzed it.
DJ Boo: Hey, I can't move!
The Shy Guy turns to Booser.
Shy Guy: Finish him!
Booser nods. He then inhales, and exhales a stream of fire. The bot gets hit and comes out burnt, along with DJ Boo. He coughs, and the bot falls apart.
DJ Boo: Why?
The Shy Guy puts his sword away while the Boos in the club surround DJ Boo.
Shy Guy: No problem. Now, I'll be on my way. Don't forget to tell Mario the message.
Booser: You got it.
The Shy Guy begins to leave, but is then tackled by a red Boo.
Red Boo: Well, looks like we came just in time. Hey Booigi! Get the other two!
Then, a green Boo comes charging in.
Booigi: You got it, Booario!
Booigi heads for Booser and Yang. Booser charges toward Booigi to protect Yang, thus getting captured.
Booser: Get out of here, Yang! I'll be fine!
Yang starts to turn and go, but just before he does, a tear appears. He then disappears. Just as he does, the door opens and the Boo police appear, along with King Boo and Princess Boo.
King Boo: WHAT'S GOING ON HERE?!
DJ Boo slowly gets up.
DJ Boo: We found Booser, some Duplighost, and that new recruit. He was undercover. This fell off of him.
He hands King Boo the camouflage disk. He observes it.
King Boo: Hmmm, looks like some technology I've never seen before. But that's not the point. Where are the intruders?
Booario: Right here, King Boo.
He turns and sees Booario and Booigi with Booser and the Shy Guy.
King Boo: ... You guys captured them?
Booigi: Yup. It was easy, too. Their guard was down, and we took the chance and captured.
King Boo: But how did you know?
Booario: We heard some noise coming from the club, so we thought that we'd investigate.
King Boo: I'm impressed. You caught TWO traitors.
Booser: Will you give it a REST?! I left the army years ago!
King Boo: Let me think... NO!
Booario: So, what do you want us to do with them?
King Boo: Hmmm.... Putting them in my castle’s dungeon is too obvious. Those Mario Bros. will find them easily...! Oh, how about we send them to Bowser's Keep, or should I say... Booster's Keep!
Booario: I like that idea.
Booigi: As do I.
King Boo: Right. Princess, please call Booster and tell him that some prisoners will be delivered.
Princess Boo: Right away.
She pulls out a Boo Phone and calls him.
King Boo: Booario, Booigi. I need you to take the prisoners to Booster's Keep so he can lock them up. And just so they don't think about escaping...
King Boo approaches Booser and the Shy Guy and points his stubs at them. A hypnotic wave appears and hits them. They are put to sleep.
Booario: Ah, the hypnosis spell. Good choice.
King Boo: Thanks. Now get moving!
Booigi: Right away, sir.
They disappear. King Boo then laughs.
Princess Boo: The call has been made.
King Boo: Excellent.
From outside the club, Yang is seen listening to the conversation.
Yang: So, that's where they are being taken.
??????: That's where who is being taken?
Yang turns around and notices a Shroob, a Yoshi, and a Blooper. The Shroob is different from other Shroobs. He has a sword sash containing a sword and has red spots on his head instead of white. The Yoshi is wearing sunglasses, has a sword sash with a sword inside, has spiky wristbands plus a spiky collar around his neck, and is black with a white under belly. The Blooper is the only one that doesn't look unusual, unless you consider a black Blooper unusual. He also has, you guessed it, a sword sash containing a sword.
Yang: Uh, can I help you?
Shroob: Yeah, tell us where your friends are being taken.
Yang: No. You have nothing to do with them! I'm outta here.
Yang jumps onto the roof and jumps from roof to roof, heading back to the mansion to tell his friends the horrible news.
Blooper: Nothing. I told you Yang wouldn't tell us anything.
Yoshi: Are you sure Booster is located somewhere in this kingdom?
Shroob: Positive. Senshi Guy told me to come here and persuade Booster to rejoin.
Blooper: Yeah, but we still don't have a location.
Yoshi: Don't worry, I was reading his mind, and I found some juicy info.
Yoshi: Like he is still looking for his sister Ying, he doesn't remember us, and Booster's location.
Yoshi: Yup. Somewhere called Bowser's Keep, only Booster renamed it Booster's Keep.
Shroob: Yes! You never fail to amaze me, Spikeshi. Bloopshi, take a look at the map. Where is this Bowser's Keep?
The Blooper, Bloopshi, takes out a map of the Mushroom Kingdom. (Yes, I meant the Mushroom Kingdom. King Boo only took over the castle and Toad Town, not the entire kingdom.)
Bloopshi: Let’s see... Ah, it is east of Gusty Gulch.
Shroob: Very well...
He puts his claws together and forms a portal. The three of them go in.
Back at the mansion, the heroes are seen eating lunch. Jr. is seen at the BBQ cooking hamburgers. Everyone is enjoying them. Then, Yang comes running through the forest and rushes up to them, panting heavily.
Mario: How did it go? And where's Booser?
Yang is silent.
Yang: He... was... captured.
Yang: Yeah, and that Boo Guy, who isn't even a Boo. He's a Shy Guy with great power.
Jr: A Shy Guy with great power?
Yang: Yeah. But that's not the point. The point is that we have to save them!
Luigi: How? We still have to find six Crystal Hearts.
Yang: Oh, yeah... the message was that King Boo has one. So there are five left.
Yang: Come on, guys, focus! We have to find a way to save them.
Mario: ...! I know. We have to do this while looking for the Star Portal pieces. We split up. One team goes and looks for the Heart. The other team saves Booser and the Shy Guy.
Yang: I like that. Okay, I'll be the leader of the Booser search party.
Luigi: I'll go with you. Me and Booser took down King Boo together.
Yang: Awesome. Anyone else?
Jr: I'll go. You guys will need a powerhouse.
Luigi: ... You know, that sounds like something your dad would say.
Jr: I know.
Mario: Great, so me, Mallow, Geno, and Kamek will go and search for the Crystal Heart.
Yang: Yup. Good luck out there.
Mario: You too.
Kamek: Come on, into the Cruiser!
Mario, Mallow, Geno, Kamek, and the troops pile onto the Cruiser and head for Starborn Valley to find the location of the next Crystal Heart.
Yang: Okay, let's go.
Luigi: But we don't know where they are being imprisoned.
Yang: Oh, I don't think so. Like I said, I am a very powerful ninja, as well as a crafty and sneaky one too. I overheard King Boo telling Booario and Booigi to take them Bowser's Keep... or should I say, Booster's Keep.
Luigi: Are you... done?
Jr: Yup. Let's go!
Yang and the party head for Booster's Keep by heading through a different part of Forever Forest and walking along Bowser's Path.
At the entrance to Booster's Keep, Booster is seen with Booario and Booigi, who have a sleeping Booser and Shy Guy.
Booster: Ah, right on time. Just take them to the dungeon with those Koopa Brats and Bowser.
Booario: Right away, Booster.
Booster: Thanks, and then report back to King Boo.
Booigi: Will do.
They head inside the Keep. Booster laughs and goes toward the Keep, but is stopped when he hears a portal appearing. He turns and sees a Shroob, a Yoshi, and a Blooper.
Booster: ... Are you guys...?
Shroob: Booster. Long time, no see.
Booster: Bloopshi. Spikeshi. Shroobiorra. You guys are all right! I knew that if Senshi Guy was fine, you would be too!
Shroobioora: Yes, it's true. We have broken Merlan's frozen prison. The question is, how did you? When we broke it, you were nowhere to be found.
Booster: Yes. Well, Merlan had frozen me in time when I was in my robot. But a few years after he froze us in time, a Boo King and a red and green Boo found my bot and took it back to their mansion. When they opened it up, they found me frozen. The Boo King used a spell that broke Merlan's, and I was free. I asked what time period it was, and they told me 2009. I asked who they were, and they told me their names were Booario, Booigi, and King Boo. I told them who I was, and I told them I had nowhere to go. King Boo told me that the reason they unfroze me was because they were looking for new recruits. King Boo told me that one day, Boos would conquer the world, and as you know, I have loved world domination ever since I joined the Senshi. So I joined, and here I am, general in King Boo's army.
Spikeshi: Interesting. Well, we have some great news.
Bloopshi: Yeah. Booshido has found another dimension for us to live in.
Booster: Is it somewhere in this kingdom?
Booster: I've grown fond of this kingdom.
Shroobiorra: Yeah, I think it is somewhere on the outskirts of this kingdom. So, are you in or out?
Booster: I don't know...
Spikeshi: You don't have to rush. Here...
Spikeshi hands him a communicator.
Spikeshi: Just use this and call us whenever you feel like joining back.
Booster: You’re leaving already?
Shroobiorra: Yeah, Booshido just sent us out to find you and see if you had changed your mind.
Booster: Well, it was nice seeing you again. I'll give you a call.
Bloopshi: ... All right.
Shroobiorra opens a portal to take them back to their new home.
Booster: It was nice to see those… GREAT!
He looks into the distance and see Yang, Luigi, and Jr.
Booster: Now I have these guys to deal with! Although, it wouldn't be too bad of an exercise.
Eventually, Yang, Luigi, and Jr. reach Booster's Keep. When they arrive, they see Booster.
Luigi: Booster! We know you are holding Booser and a Shy Guy in your dungeon!
Booster: It is true. But to get to them, you're going to have to go through me.
Yang: If going through you is what we have to, then so be it!
Booster: That's what I like to hear.
They get into fighting position and charge toward each other.
Booario: All right, in you go!
Booario is seen throwing Booser into a dungeon cell, along with Booigi throwing the Shy Guy in.
Booigi: Hope you like it in there, because that's where you will be staying for a long time. And just so you can't escape...
Booigi goes over toward the wall and pulls a lever. All the bars on every cell become electrified.
Booigi: These bars are now electrilized. If you try to escape or turn invisible, you will be shocked with 1,000 volts!
Booario: Now you REALLY can't escape.
They both leave, laughing. Booser floats toward the bunkbed in the cell and sits down on the bottom one.
Booser: This stinks! There is no way for us to get out.
Shy Guy: ... Hey, what's your name?
Booser: ... My name? It's Booser. What's yours?
Shy Guy: My name is... Blade Guy.
Booser: Blade Guy?
Blade Guy: Yes. I am here to make sure that this King Boo doesn't bring back a powerful evil by using two dark objects.
Booser: I thought you said you were looking out for Mario and Luigi to make sure they were powerful enough?
Blade Guy: That was just a cover story. I just needed to make sure that this king doesn't bring back the worst evil possible.
Blade Guy: Yes.
He takes out a piece of paper that has writing on it. There is much written on it, but Booser only sees "The King of Boos" written. Blade Guy crosses it out.
Blade Guy: Well, that's one down, now, if only there was a way to get out of here.
Booser looks at the distance between his and Blade Guy's cell and the lever Booario pulled. The cell is about two cells down from the lever.
Booser: I think I have an idea.
BOSS BATTLE: Booster
Yang jumps up high and fires a shuriken at Booster, who pulls out his jester stick and creates a force field to block the attack. He then points his stick at them and fires a beam of energy. Jr. jumps in and spins his paintbrush around to block the attack. He then flings paint onto Booster, who is hit and sent to the ground, stuck. Luigi then takes out his hammer and starts whacking Booster, who is defenseless. He then opens his mouth and flings his tongue at Luigi's face. He is licked and paralyzed. Booster then focuses his energy and gains control of the paint.
Yang: What kind of Boo are you?
Booster, who has his eyes closed and is floating high in the air, slowly opens them while giving off a glow.
Booster: A legendary one.
He then swings his arms toward Luigi, who is still paralyzed, and paint is fired at him. Jr. acts fast and flings paint to counterattack the paint Booster flung. While that is going on, Yang rushes in and pulls Luigi out. He then finds a certain spot on him and cracks it. Luigi regains mobility.
Luigi: Thanks. Now, where were we?
Luigi jumps up and whacks Booster with his hammer, into the pool of lava surrounding the Keep. Booster then flies out, all red. He pulls out his stick and releases fire bolts – bolts of lightning that burst into flames when they make contact. Booster makes a large circle of fire bolts around Yang, Luigi, and Jr that burst into flames when they hit the ground. The three of them are trapped inside. Booster flies up above the ring and laughs.
Booster: Bwhahahahahaha! This was all too easy. But it is time to finish this!
Booster, still red, starts spinning and ignites. He is a flaming Boo now. He charges toward Yang, Luigi, and Jr to finish them off.
Booster: SAY GOODNIGHT, YOU WORTHLESS HEROES!