Mario
The new trio soared towards the observatory. As they got closer, they watched as the airships fired on the observatory, and Mario could just barely make out Rosalina's figure fighting back.
"Alright!" He shouted in an attempt to be heard over the wind. "We've got to figure out which ship King Boo is on, so I say we split up."
"But how will we know when someone's found it?" Luigi asked.
"Actually, I feel like I already know where he'll be," said Bowser Jr. Mario looked at him in surprise, but nodded. "He'll be on the Wrecker, my dad's personal ship. You'll know it's the one because it's the largest out of all of them."
"It's worth a shot. And I think that's it," Mario gestured towards an airship that was definitely larger than the rest of them, and began flying towards it when suddenly the jetpacks began to beep. "It's gonna be close!" He warned Luigi. Luckily, they barely made it over the guard rail, and found several Koopa Troopas working the cannons.
"Intruders!" One of them called out. Mario knocked him unconcious, but the damage was done. Soon hundred of minions were swarming the deck, and the group was surrounded within minutes.
"Well, now what?" Luigi whispered.
"Allow me," Junior replied. He pulled out the brush and spun it around, blinding the enemies closest to them. Leaping into the air, he transformed into Shadow Mario, stomping on most of the minions while Mario and Luigi to take advantage of the chaos. Unfortunately, they'd forgotten about the Boos possessing the minions.
"My turn," Luigi grinned as he activated the Poltergust, vacuuming all of the Boos within an instant. Soon, the deck was cleared, and they began to make their way to the cabin. Before they could even open the door, however, they were blown back by a blast of lightning as King Boo marched out of the cabin.
"Well, well, well, I never expected someone like you to betray me, Junior," he sneered.
"When I agreed to work with you, I never meant that you could possess the entire army! Plus, you never cared about me from the start."
"That's not true at all! I've helped you so far, haven't I? You're the one that decided to go and team up with your father's killer!" At this Junior could only frown.
"It's a temporary arrangement. Besides, you're one to talk, considering the body you're using right now!"
"This form was a mere stepping stone in my master plan. In fact, I could abandon this form right now, but I'm not that dumb. I know what that vacuum on your back does," he said, pointing at Luigi. "Now, Junior, I'll give you one last chance. Help me destroy these pesky plumbers and the observatory, and you will be spared when I recreate the universe!"
"...What?" Mario exclaimed.
"Please, Rosalina already told you who I really am. I seek to destroy the entire universe and recreate it with me as its sole ruler!"
"But what do we have to do with your plan?!"
"At first, nothing. To reset the universe, I simply need the power of the Lumas. My first attempt was almost successful, but they were scattered all across the universe. By the time I found them, they had found a new mother. I engaged her in battle, only to be defeated and cursed to this ghostly form. I then realized if I wanted to succeed, I needed an army, so I waited. Years passed, until I finally met your father." He turned to Junior, who was now preparing to wield the brush. "More specifically, it was his spirit. He told me his story, and I offered him another chance at life. In exchange, should he die again, I would be given his body. The fool agreed, and all I had to do was continue to wait. Sure enough, Mario finally came through and killed him, allowing me to start the plan I had started years ago." King Boo laughed, as if realizing the irony of the situation. "By killing one evil, you unleashed a far greater evil! With my army, I will now take control of the Lumas! So, I will ask you one more time, Junior. Are you in, or out?" Junior looked back and forth between the King and the Mario brothers. This was his last chance to decide who he truly wanted to be. He turned back to the King.
"My father may not have been the best person, but he would never stoop to your level." He whipped out his paintbrush and leapt into the air. "Let's go!" He shouted as he brought the brush down toward King Boo's head. Before he connected, however, a purple blade materialized in the King's hand, which blocked the blow and sent Junior flying back across the ship. Mario and Luigi assumed defensive stances as Junior got back up.
"Here, you might need these," he noted as he painted some fire flowers for the brothers. They each grabbed one, absorbing their power and returning their attention to King Boo.
"I see how it is. Let's fight fire with fire!" The king inhaled and shot a plume of fire from his gaping maw. Everyone jumped out of the way until the fire disappeared. Mario jumped over the king and shot a fireball, which was blocked by his blade. Luigi attempted the same thing, but King Boo summoned another blade to block it. Now wielding two blades, he shot a blast energy at each of the brothers, which they narrowly dodged. Junior ran in for another attack, this time transforming into Shadow Mario. He launched a barrage of paint at the king, catching him the eyes.
"Ah!" He shouted, staggering back and losing the blades. Mario and Luigi nodded, and locked hands as they focused their energy on summoning a massive fire.
"Now!" Mario shouted. They released it, and King Boo was launched over the side of the ship.
"Noooooo!" He shouted as he plummeted down to Earth.
"Did we do it?" Junior panted. Immediately after he said those words, however, the ghostly form of King Boo rose into view.
"You IDIOTS! YOU'VE ONLY MADE ME EVEN MORE POWERFUL!" Thunder boomed as clouds rolled in over the ship. "NOW YOU WILL DIE!" Instantly, hundreds of bolts of lightning began to barrage the ship. Luckily, Bowser Jr. had just enough time to paint a shield, but it didn't look like it would hold for long.
"Any ideas?!" He shouted. Suddenly, the noise stopped. The paint disappeared, and it was then they noticed that the sounds of battle had stopped. Rosalina hovered in the air, staring down King Boo.
"Face it, you've lost. You're only stalling for time in a vain attempt to keep from entering the vacuum."
"NEVER! MY PLAN WILL SUCCEED! I-" There was a whirring sound as Luigi activated the Poltergust, aiming it right at the king.
"I'm ending this now!" He shouted.
"Wait! No!" King Boo screamed as he was dragged closer to the Poltergust. "I'll escape! I'll be back! Just you wait-" He was cut off as he was finally sucked inside, never to be heard from again.
"Well, that wasn't so hard," Luigi commented. No sooner than the words left his mouth, however, the ship began to shake. The purple light that had previously enveloped all of the airships disappeared, and one by one they began to fall back to Earth.
"We have to get out of here!" Mario shouted.
"But the jetpacks are out of fuel!" Luigi replied.
"Allow me," Rosalina called out. A bubble formed around each of them, carrying them over to the observatory. They were deposited on the platform, and everything seemed okay until...
"The castle!" Mario screamed as he watched the airship they had just been standing on head directly for the castle. "Peach is still down there!"
"You'll never get there in time, even with my help..." Rosalina whispered.
"They might not make it, but I can." Junior painted a glider and leapt off of the observatory, soaring back to Earth. He closed his eyes as his body was enveloped in heat, but he was determined to prove himself one final time. Finally, he landed in front of the castle, but the airship was rapidly closing in. Closing his eyes, he took a deep breath, preparing to make his best work of art yet. He swung the brush in a rapid motion, quickly forming a barricade as the airship got closer and closer. Finally, at the last second, he closed off the barricade that would take the brunt of the impact from the airship. "Let's just hope it's strong enough..." he whispered as the world crashed down around him.
Author's note: Okay, I changed my mind, epilogue coming soon!