In the Mushboo Kingdom, King Boo is laughing with joy.
King Boo: Bwhahahahahahahahahaha! I can't wait to take down those Mario Bros. once and for all!
Princess Boo: Honey, don't you think it's dangerous to put yourself on the line?
King Boo: Oh sweety, me taking them down is a backup plan. The real plan is...
He whispers into her ear, if she has one. She then gasps.
Princess Boo: No! You can't.
King Boo: Don't worry, my dear, there is no way they will fight if I do that.
Princess Boo: Really?
King Boo: Yes, that is why this plan is foolproof!
Then, a Boo guard shows up.
Boo Guard: Sir! Our sky patrol just spotted the Koopa Cruiser heading this way! What should we do?
King Boo: Let them land, but have the “welcoming” committee setup in the castle.
Boo Guard: Yes sir.
He rushes off.
King Boo: Hehehehehe.
***
Kamek: Now, fire at will!
A Koopatrol pushes a button and it activates the Bullet Bill cannons. They are fired toward the ground and knock out the Boo guards. The Cruiser lands and Mario, Luigi, Booser, Yang, Mallow, Geno, and Jr. walk out.
Jr: Kamek, if anything happens out here, take out any Boo you see.
Kamek: Yes, my Prince.
He shuts the door and the heroes advance toward the castle, which looks exactly like King Boo's old mansion, only inside, it is a haunted version of Peach's Castle.
Mario: Well, this is it.
Mallow: If anything happens, I just wanted to let you guys know that you are my best friends.
Geno: Same here, buddy.
Luigi: All right, lets go!
Luigi heads for the door and tries to open it, but can't.
Luigi: They must've locked it.
Yang: Allow me.
Yang reaches into his robe and pulls out a bomb shuriken. He throws it and it blasts the door wide open. The seven of them enter and find it very haunting.
Booser: Wow.
Yang: King Boo sure redecorated this place.
Luigi: No time for that now, we have to find King Boo!
Mario: My best bet is that he'd be in the throne room.
Mallow: To the throne room!
??????: I don't think so!
Geno: What the?
A Boo with glasses appears in front of the heroes.
Boo: I am under the orders of King Boo and I'm not supposed to let anyone pass.
Luigi: Who are you?
Boo: I am Prof. Boo, the scientist of King Boo's Army.
Mario: So you're the one who built Booster that Boo in the Box.
Jr: And the Boo in the Box 2.0.
Booser: And that bot for DJ Boo.
Mallow: Along with that mechanical mallet for Booario.
Prof. Boo: Hmmm, you learn fast. But all those machines... useless! They are just a pile of junk! Let me show you a real machine!
He grabs a remote and presses a button. From below them, a giant Boobot with red, robotic eyes and a sharp, mechanical mouth comes out of the ground and floats off the ground. Prof. Boo jumps in and pushes a button inside the Boobot. From below it, a hole opens up and gains a rim, and eight robotic tentacles with razors at the ends appear.
Prof. Boo: Say hello to my greatest invention! Meet OCTOBOO!
Mario: Well... this is bad.
Luigi: Come on, we can do this!
Yang: Let’s go!
BOSS BATTLE: Prof. Boo in the Octoboo
Prof. Boo starts pushing buttons and the Octoboo responds by sending out one of its tentacles at Mario, who smacks it away with his hammer. Luigi then grabs his own and starts running toward the actual robot and starts hitting it. One of the tentacles comes up to Luigi and smacks him off. Mallow starts hitting his Sonic Symbols together, creating a shockwave that messes up Octoboo's controls. He starts swinging his tentacles around randomly.
Yang: HEYA!
Yang jumps up and throws a static shuriken that hits Octoboo square in the center of his face. He starts giving off static and is having a hard time moving.
Booser: Some machine you got there!
Prof. Boo: Don't worry, I came prepared!
He pulls out a small metal box and sticks it on the back of Octoboo, which starts swinging his tentacles and is moving a lot more easily.
Prof. Boo: With that refresh box on his back, you can't inflect any conditions on him or cause him to malfunction! Now take this!
Octoboo turns to his side and starts spinning like a pinwheel. He heads for Jr, who jumps out of the way and shoots globs of paint on the tentacles, making them sticky and unable to move. But the refresh box activates and opens up, revealing a fire hose that sprays the paint off with water.
Jr: Crud.
Geno starts shooting his Star Gun, but Octoboo swats the stars away, then shoots a black substance. Geno dodges it, but when the substance hits the ground, it burns through the floor. Geno notices.
Geno: What kind of substance is that?
Prof. Boo: Hehehe. A little chemical I call Super Ink. It has the power to burn through stuff. Unfortunately, it is also very flammable.
Booser: Flammable... I think I know how to beat him.
Booser flies up above him and taunts him.
Booser: Bet you can't hit me with your Super Ink!
A small hole opens up on Octoboo's head and shoots a ton of Super Ink. Booser dodges. The Super Ink burns through the ceiling and goes all the way through the roof. Then it starts raining back down onto Octoboo. Prof. Boo starts panicking.
Prof. Boo: Oh no! What am I going to do? The Super Ink will... not affect me! HA! I made this robot with a powerful steel that cannot be burned or dented.
Booser: I wasn't trying to burn the robot with the Super Ink!
Prof. Boo: Huh?
Booser inhales, then exhales a large stream of orange fire. He makes contact with Octoboo, who begins to catch on fire.
Prof. Boo: NOOOOOOOOOOOOO! The Super Ink will have no affect on my Octoboo, nor will a regular flame breath. But when combined... I'M DOOMED!
Booser: Geno! Yang! Finish this!
Geno uses Geno Blast, and Yang sends an exploding shuriken. The two attacks make contact and cause Octoboo to explode, sending Prof. Boo flying. He hits the ceiling and crashes down on the ground.
Prof. Boo: Ohh... Why? How could I lose? I built Octoboo with the BEST type of metal and gave him some good weapons. I have failed, King Boo...
Mario: We are done here. Let’s go, guys.
Mario and Co. leave, but Luigi stays behind and heads toward Prof. Boo. Then all we can see is Prof. Boo next to Luigi's shadow, which is about to bring something out.
Prof. Boo: Hey, what are you... no. Not that! Please, anything but that! NOOOOOOOOOOOOO!
All that is heard is a slurping noise. Then Luigi rushes to catch up with the others.
The heroes find themselves in a room filled with five empty paintings and two lit candles.
Luigi: I don't remember this room in Peach's Castle.
Then the five empty paintings jiggle and lift into the air. Then they head for Mallow, Geno, Booser, Yang, and Jr. The five paintings smash them, and when they lift off the ground, the five of them are trapped inside the paintings.
Luigi: What is going on?!
??????: Don't worry, we will make this quick and painless.
Then a red Boo and a green Boo appear in front of the paintings.
Mario: Booario!
Luigi: And Booigi too.
Booario: Yes, we are next in the line of defense to prevent you from getting to King Boo!
Booigi: And we only want to battle you two, no one else!
Booario: Yeah, ever since you beat us, we have wanted revenge!
Booigi: Especially me! Ever since you guys beat King Boo a little while back, I wanted to beat you ever since!
Booario: Now that we have all that covered... IT'S TIME TO GIVE YOU A TASTE OF YOUR OWN MEDICINE!
BOSS BATTLE: Booario and Booigi
Booario starts by flying toward Mario at high speeds. Mario dodges and grabs his hammer. He charges after Booario, who does a flip to avoid heading into the wall and comes back for more. But this time, he sticks out his tongue and licks Mario right in the face. Mario can't move.
Booario: Hehehehehehe. Time to show you something I found in your house!
Booario grabs an Ultra Hammer and a Lazy Shell.
Booario: Time to end your game!
Mario struggles very hard to get moving again, but to no avail. Booario puts the Lazy Shell on the ground and is about to smack it with the Ultra Hammer. He swings back, and hits it with great power. The Lazy Shell heads fir Mario at top speed. Mario tries again to move, and this time, he regains mobility in his arms. He swings his hammer and smacks the Lazy Shell back at Booario.
Booario: Uh oh.
He is hit with the shell and sent into the wall. He goes through and hits something hard. He looks at his surroundings and notices he is in Prof. Boo's lab. He sees an invention that catches his eye…
***
Luigi and Booigi are going at it by smacking each other with their hammers. Booigi them starts spinning around while swinging his hammer. He goes out of control and is moving everywhere. Luigi throws his hammer like a boomerang at Booigi and hits him. He is knocked out, or so Luigi thinks. While Luigi has his back turned, Booigi inhales, then exhales a stream of green fire.. He hits Luigi. Luigi turns and gets angry.
Luigi: You wanna play like that? Fine.
He pulls out a Fire Flower and turns into Fire Luigi.
Booigi: Ah, a fire battle. Then let it be!
***
Mario goes and picks up his Ultra Hammer and looks at his hammer he bought from Hinopio. It broke in half when he smacked the Lazy Shell back. He throws the old hammer away and takes his Ultra Hammer.
Mario: Now where's Booario?
Booario smashes through the wall and comes out with body armor and sporting a Bullet Bill cannon on his head.
Booario: Now let’s see who can beat who!
Booario fires a Bullet Bill. Mario rushes toward the Bullet Bill and smacks it with his Ultra Hammer. Booario charges toward Mario and headbutts him, which hurts really bad. Mario is sent into the wall. He then lands next to the Lazy Shell.
Mario: Time to pull of my best combo.
Booario comes charging at him again, but Mario is prepared. He swings and smacks the Lazy Shell. It hits the armor and cracks it. Then, it just breaks, leaving a scared and exposed Booario. Mario rushes up to him and whacks him with his Ultra Hammer. Booario is sent into the wall, fainted.
***
Luigi and Booigi are seen shooting green fireballs at each other. Booigi then shoots a stream of green fire. Luigi shoots a giant fireball at the stream. They make contact and explode. Booigi rushes through the smoke and headbutts Luigi to the ground. Luigi gets back up and fires a barrage of fireballs at Booigi, who doesn't have enough time to counterattack. Booigi is hit and set aflame, but uses this to his advantage. Booigi charges toward the fireballs while burning. He then headbutts Luigi again, this time while still on fire. Luigi is hit and loses his fire power.
Luigi: Nooooo!
Booigi: Ha! I used your fireballs against you. Time to end this!
He inhales, and shoots a stream of fire. Luigi then gets up and runs his hammer through the stream. He then makes it to Booigi, jumps, and smacks him on the head really hard. Booigi starts to sway back and forth until he finally faints.
Luigi: And I just used your tactic against you.
The four paintings starts shaking and break. Mallow, Geno, Booser, Yang, and Jr are freed.
Jr: Way to go, guys!
Yang: Nice job.
Booser: Couldn't have done it better myself.
Mario: Thank,s guys.
Geno: Come on, guys, let’s get going.
They head through the door, but Luigi stays behind again and does the same thing he did to Prof. Boo. He catches up with the others and they all find themselves in a large ball room. Then, Boolossus appears.
Luigi: Boolossus! We haven't seen you this entire adventure. I thought King Boo fired you?
Boolossus: Well, you thought wrong! I am second best in King Boo's Army. Booster might be the first, but that is only because he is a legendary Boo. Anyway, King Boo ordered me to stop you guys, and that is what I am going to do!
He raises his stubs and they begin to glow. Nobody except Geno knows what he is going to do. Boolossus fires a blue beam. Geno then gets wide-eyed.
Geno: Look out!
Geno only manages to push Mallow and Jr. out of the way. Mario, Luigi, Booser, and Yang are hit by the beam.
Boolossus: Drat!
Mallow: What was that?
Geno: A bind blast. It paralyzes the enemy when hit.
Jr: Thanks for saving us. Now, let’s get him!
The three of them charge toward Boolossus.
BOSS BATTLE: Boolossus
Geno fires his Star Gun at Boolossus, who counterattacks by firing mini Boos to take the hit. Mallow then uses his Sonic Symbols and Jr. flings paint. Boolossus fires an ice beam that stops the attacks and hits Mallow and Jr. Geno then fires his Geno Beam, but Boolossus opens his mouth wide and eats the beam. He then sends the beam back with twice the power. Geno is hit and sent into the wall. Geno gets up and rushes back to Jr. and Mallow to retaliate.
Mallow: This guy is insanely tough. He’s blocked all of our attacks.
Geno: There has got to be some way to hurt him.
Jr: I played Luigi's Mansion with Lemmy and Iggy.
Mallow: Okay, so how do you hurt this guy?
Jr: Uh...! Oh, when he was bouncing around, he had to hit something spiky.
Geno: Something spiky?
Geno looks at Mallow and they nod and turn to Jr.
Jr: What?
He looks at his shell.
Jr: Oh all right, but only because I am the source of spikes.
He tucks into his shell and Mallow picks him up and throws him at Boolossus. Boolossus questions what they are doing and laughs at the fact that a shell will not leave a dent in him. But when he is hit, he bursts into 15 Boos. All the Boos then begin to float around screaming. The three heroes starts sending their attacks at the Boos. They only manage to hit six, leaving nine left. The nine Boos regroup and form Boolossus again. He is a bit smaller than before, but still packs a punch.
Boolossus fires another ice beam, but Geno protects the three of them with Geno Whirl. The two attacks collide and explode. Boolossus charges toward the smoke and hides. When he sees three figures, he goes and shoots a lightning bolt. It explodes on the ground in front of them and sends them flying. Then Boolossus blows away the smoke and quickly turns invisible. When the three heroes get back up, they don't see Boolossus. Jr. then gets an idea.
Jr: PAINTBRUSH EXPLOSION!
Jr. starts spinning around rapidly, flinging globs of paint that fill the entire room. When Jr. finishes, he becomes dizzy and starts stumbling around. Mallow and Geno takeover and look around for floating paint. They find a giant, round glob of floating paint. They figure it is Boolossus, so they attack with Shocker and Geno Blast. They hit the glob and it indeed turns out to be Boolossus, who becomes dazed. Geno grabs Jr, who is still dizzy, and throws him at Boolossus, who gets hit and bursts. Geno and Mallow use their Star Gun and Sonic Symbol attacks to take down more Boos. They only manage to get four Boos, leaving five left. The five Boos regroup and form Boolossus, who is just about double the size of a regular Boo.
Boolossus begins to steam with anger and rapidly fires ice beams everywhere. He then freezes the entire room. Jr, who is no longer dizzy, begins to shoot fireballs. Boolossus, being much smaller, is now much faster, able to dodge a lot more attacks. He raises his stub and forms a lightning bolt. He fires it, but Mallow jumps in and brings out his Sonic Symbols. He clings them together with the lightning bolt between them. When he opens it, his Symbols are electrified. He uses them and the soundwaves are also electrified. They hit Boolossus and he becomes paralyzed. Mallow grabs Jr. and throws him. Jr. hits Boolossus and he bursts into the five remaining Boos. Mallow performs Star Rain and Geno performs Geno Blasts. Stars and colorful blasts of light rain down on the Boos. When the attacks finish, all fifteen Boos are seen knocked out.
All Three Heroes: YEAH!
They look toward the other four, who are beginning to regain mobility.
Mario: Way to go, guys!
Luigi: Yeah. You really pulverized Boolossus.
Booser: I wish I was in the fight. I've wanted to show Boolossus a thing or two ever since me and Luigi beat King Boo last time.
Mallow: We have beaten every one of King Boo's troop members. That only leaves him left.
Yang: Wrong. There is another.
Geno: What do you... Oh.
Yang: Yes. Booster is the last one.
Jr: Then let’s go kick his behind!
All of them walk off, except Luigi, who stays behind.
Luigi: All right, let’s make this quick.
He is about to grab something, but before he does that, he turns and sees that the fifteen Boos are gone.
Luigi: What the?
He catches up with the others. But then, the fifteen Boos reappear. They turned invisible as the heroes walked off.
Boo #1: That was close.
Boo #10: Yeah, we almost suffered the same fate as Prof. Boo and Booario and Booigi.
Boo #7: What are we going to do now?
Boo #5: We head back to Boo Mansion with what troops we have left. We shall be the new king until King Boo returns.
Boo #4: And if he doesn't?
Boo #6: We find out what happened to him, and free him.
Boo #2: I like that idea.
Boo #3: Now, let’s form back into Boolossus and round up all the troops.
Boo #11: I agree.
They form back into Boolossus and round up the troops so they can head back to the old mansion.
***
The seven heroes enter a room that is filled with nothing but lit candles. They advance to the center of the room. Then, they hear laughter. A jester stick then appears and spins around. Then, out of thin air, Booster appears, holding the jester stick.
Booster: Welcome, to the final room! You have made it this far, but this is where it ends. Prof. Boo, the Boo Bros, and Boolossus were nothing but worthless minions. They are nothing compared to ME!
Mario: Let’s get him, guys!
Booster: Not so fast! I only want Yang in this fight!
Yang: Me?
Booser puts his hand on his shoulder.
Booser: If Yang is fighting, then I'm fighting alongside him!
Booster: Hmmmm, you seem determined to fight along side him. I can feel it. Go ahead if you want, but it won't make a difference. Just to make sure no one else helps...
He points his jester stick at the remaining heroes and fires a yellow beam that creates a forcefield around them so they don't escape.
Booster: That forcefield will keep you from helping, Yang.
Yang: Let’s get this over with. We have a princess to save, and some Crystal Hearts to get!
Booster: Let’s get this over with... You took the words right out of my mouth.
Yang pulls out an icy blue shuriken and throws it at Booster. Booster smacks it away with his jester stick. He then spins it and creates five energy balls. They head for Booser and Yang. Booser jumps in and turns both of them invisible. He then reappears and fires a stream of fire at Booster. Booster, who was surprised by the quick counterattack, is hit. He comes through the attack somewhat burnt. He grabs his jester hat and points it at Yang and Booser. He then shoots out a large magical beam. Booser avoids it in time, but Yang is hit and sent headfirst into the wall. He is then knocked out. Booser turns and sees him knocked out.
Booser: YANG!
He is then hit with an electrical blast from Booster's jester stick. He faints.
Booster: All too easy.
He then approaches Yang and points his jester stick at him.
Booster: It's time to finish what I should've done a long time ago.
A bulb of light appears at the end of the stick.
Booster: Say goodnight, Yang.
A lot is rushing through Yang's head right now. We go deep into his thoughts and see him as a spirit observing a battle involving him, as another Duplighost fights beside him. This Duplighost has the opposite color scheme of Yang. Everything that is black on Yang, is white on the other. Everything that is white on Yang, is black on the other. And this one is a female, you can tell because the Duplighost has a bow on her. They are both fighting against Booster.
Yang and the other Duplighost use a ninja skill that all high-level ninjas can perform. This destroys Booster and sends him to the ground. Yang and the other Duplighost approach him to finish him off, but Booster gets an evil grin and pulls out a diamond-shaped crystal. It then lets off a large beam that doesn't hurt, but absorbs the power and soul of the victim. The beam hits Yang and he starts to be slowly absorbed into the crystal. The other Duplighost then charges toward Yang and tackles him out, taking Yang’s place of being absorbed into the crystal.
Yang: YING!
Ying, the other Duplighost, is seen giving off her last smile as she is absorbed into the crystal. Once finished, Booster laughs and is about to leave with the crystal. Yang then gets angry and throws a bomb shuriken at the crystal. He hits it right on the mark and it explodes into eight pieces. The pieces then disappear. Booster is only able to obtain one piece. He gets angry and fires a beam at Yang that sends him into a tree, headfirst, causing him to lose his memory. Booster disappears.
The Yang spirit that has relived this tragedy gets fire in his eyes. We now see a fainted Yang about to be finished by one final attack from Booster. Just as Booster fires the beam, a forcefield appears around Yang. The beam bounces off.
Booster: What the?!
Yang slowly gets up and makes the forcefield disappear. Booster sees fire in his eyes.
Yang: I remember. I remember all of it!
Booster: What are you talking about?
Yang: You were the one who took my sister's life away from her!
Booster: What are you... oh. That. Hey, it was her own fault for trying to save you! If she hadn't, you would've been trapped in that power crystal.
Yang: She saved me because she loved me. And she loved me because I am her brother! It's called sibling love!
Booster: You know, ever since I knew you were with these Mario Bros, I wanted to show you something.
He reaches into his jester hat and pulls out a small, diamond-shaped crystal.
Booster: This is the same piece of the power crystal that you broke long ago. I've kept it so I could find the others, put them back together, and obtain Ying's power, thus making me the most powerful being in the world!
Yang: ... You're a... MONSTER!
Booster: Oh, so you're calling me a monster? Well, let me show how much of a monster I am!
He puts away the crystal and grows to a large size, obtains a long snake body with two large bat wings on each side, longs arms, larger hands with three claws on each hand, and a head that looks like Rayquaza's, meaning he has horns on his head. His voice also becomes deeper. The heroes in the forcefield are frightened.
Booster: BWHAHAHAHAHAHAHAHA! You think I'm a monster, then here I am! A monster! Also called my release form! This is why I'm the best Senshi in Booshido's Senshi!
Yang: You might look like a monster now, and you might be more powerful, but I am still going to beat you! FOR MY SISTER!