In Bowser's Castle:
"Sir," one of the Hammer Bro soldiers said, "our resources have gathered that King Boo, who bears the key, is gone."
"Gone?! Dafuq, what do you mean, 'gone'?" Bowser roared in rage. He didn't like what he'd just heard.
The Hammer Bro soldier tripped back a few steps. "Uh, what I meant to say was...Your Highness, according to our Parakoopa troops, they have ibingiay us intelligence that King Boo is no longer where he is."
"Well, where is he?"
"He's not around...It's as if...he's really gone, like he's dead?"
"Who could've done that?!"
"I don't know for sure, Your Highness..."
"Dumb fuck, you should know!" Bowser snapped.
"It's quite...unclear, Sir. The reception was all messed up—"
"You're the one who'll get messed up if you goddamn don't figure it out!"
"Something messed up the reception—or rather, someone did. Apparently King Boo wasn't the only one around in the mansion when he was last there. Whatever he did, he jammed it up—his activity got in the way of our contact with King Boo."
"And I don't suppose you know...?" Bowser was getting pretty impatient now.
"Well, we tried to bring the recorded samples of the jammed reception to our Koopa Intelligence Resources, and upon converting the scraps of messed up soundwaves, it would appear that what showed up on the monitor screen was...a vacuum-shaped backpack, a green tail and a hat."
Bowser, who'd been wanting to go on a rampage on the Hammer Bro, suddenly fell into stunned silence. He pondered over the three clues that were deciphered sa pamamagitan ng the KIR. Vacuum-shaped backpack...green tail...hat...
Bowser stood up with a disgruntled expression. "It's them."
"Pardon, Sir?"
"The green twosome! The pipsqueak's brother and his pet lizard."
"Were you referring to...Luigi and Yoshi...?"
"Duh, who else! How else do you think they weren't around when we ambushed Peach's Castle?! Did you think they were off to a likely coincidence on a vacation?!"
The Hammer Bro flinched.
"They weren't around when we ambushed Mario and the rest of them. But those two—they were probably around to know it happened, but odds are they'd gone to hiding. Huh—those two are lucky to have escaped my clutches, but not for long."
"They probably got the key already," the Hammer Bro said.
"Well, they better not think that just because they can hack their way into my kastilyo it means rescuing their little pals will be a total cakewalk! In fact"—Bowser cocked his head to the side and laughed evilly—"I'll make them come to feel that coming here was the biggest mistake of their lives!"
"So what do we do now, Sir...?"
"It's gonna be a slight change of plans on this one—alert the troops—the Koopas, Parakoopas, everyone! We'll give those two the welcome wagon they'll never forget!"
"Yes, Sir."

Just outside Bowser's Castle:
"Thank my very lucky stars I didn't get sick this time," Luigi sinabi as, with the help of the ever-reliable warp zones, they managed to arrive at Bowser's kastilyo faster than it takes for Yoshi to lay an egg.
"Hey, it's an improvement," Yoshi said. "Plus, you didn't bump into anything when you landed.
"That was just for the sake of not complaining the entire trip, pal."
"You would know."
"Hardy har har—anyway, so we're in front of Bowser's Castle, blah, blah, blah. And we got the gem a-needed to break Bowser's new security system, good. But then, what? How are we gonna use it to get ourselves in?"
"Have you tried the statues?" Yoshi asked. "I mean, that's where we found the clues; I'm sure that's how we'll use the gem."
"Let's try it out." Luigi looked at the two Bowser statues that where on either side of the door.
"Well?" Yoshi prompted.
Luigi turned to the green dinosaur with a wry smile. "I...don't know how we'll use it."
"Let me try," Yoshi sinabi as he took the gem from Luigi and tried to place it inside the mouth of one of the statues.
But nothing happened.
"That's just great," Luigi grunted.
"Maybe it's not in the proper position?" Yoshi guessed.
"You know what, Yoshi? I'm a-starting to think that maybe this gem isn't what we've been looking for."
"What are you talking about, Luigi?! Professor scanned it himself and even he sinabi that the codes claim King Boo's gem is the key!"
"Yeah, I know, but...Do you seriously expect us to be able to actually use this thingus to get pass this place?"
"I know the answer is somewhere around here—maybe we just need to figure it out."
"Like another riddle, huh, Yoshi?"
"Yep, exactly like that."
"Two statues, one gem..."
"How will we use this to get ourselves in...?"
"You think, sa pamamagitan ng chance, this has something to do with all the other creatures we faced?" Luigi asked suddenly.
Yoshi frowned. "I don't think so...This came from King Boo—I mean, this is his gem...I don't think there could be a possible connection with the others."
"Well, I was just thinking...when we defeated the soil-monster thing with the key-eyes, there was a clue that led us to Lakithunder, then he left out a clue that led us to the mansion to battle King Boo, and he left us with a gem to lead us back here," Luigi stated.
"Okay, so maybe they are all connected, but...is there a way for that to help us out here?"
"There has to be. I mean, this whole time King Boo had the key. We could've just gone directly to him, yet we got through all the motions with a-heading to Yoshi's Island and to World Seven just to lead us to the mansion. In short, before we could just face King Boo, we were led to those other places first."
"And you're thinking...?"
"Well, it might not have anything to do with the places, just those creatures. Look, we fought that disgusting key-eyes soil monster, then we had to face Lakithunder, who zapped lightning bolts that were too fast for us to see—"
Just then Luigi cut his sentence short. Yoshi looked at him with an alarmed expression—he knew all too well what that look on Luigi's face meant. His strange sleuthing talent had struck yet again.
"The eyes...," Luigi said, looking the eyes of the two Bowser statues, which he'd just realized where not made of granite like the rest of their bodies; they were made of small light detectors. He then looked at the gem on Yoshi's hand and something lit up on him.
"That's it, the eyes!" Luigi sinabi with joy. Yoshi jumped at Luigi's sudden outburst.
"Whoa, Luigi, I think I demand an explanation for what got into you."
"Can't you see, Yoshi? The eyes—that's what we need with the gem!"
It was then that Yoshi also took a closer look at the eyes of the Bowser statues, and gave a gasp when he also realized they were light detectors.
"But how...?" Yoshi said.
"Look, when we battled in Yoshi's Island, we had to pay attention to the eyes, specifically the key-eyes where everything will a-be over. Then there was in World Seven, where I couldn't just rely on sight since Lakithunder's lightning attacks where too fast for me to see; I had to rely on my hearing for the thunder that inevitably followed. Then there was King Boo, where he showed us all those larawan that caused us to give up; we saw them. Add to that the fact that there was the strobe light that a-blinded all the other ghosts! So since each of our battles had something to do with sight, I figured...the answer was at the eyes!"
Yoshi felt like his jaw would drop at the sheer logic behind Luigi's explanation. Then he laughed. "You know, Luigi, they really should make another game with you on the lead—I think you'll do just great on puzzle-solving games!"
Luigi laughed as well. "Huh, I'm seriously considering that. Now...let's talk madami about that after we rescue Mario and the others. Gem, please."
Yoshi handed Luigi the gem. Taking a few steps back, Luigi held up the gem so the sun's rays could reflect it; the light bounced off King Boo's gem in four different rays. Then, moving a bit to adjust the rays' direction, the rays finally found their way to the light detectors.
There was a light click that resulted, then a light rumble followed.
"Whoa," Luigi said.
"Yikes," Yoshi mumbled.
The rumble only lasted for a minute, then the massive kastilyo door opened.
Luigi and Yoshi tensed. They didn't like the sudden atmosphere going on behind the kastilyo door.
"I've got a bad feeling about this, Luigi," Yoshi said.
"Me too—but we're going in!" Luigi sinabi as he and Yoshi went in.