While walking through the gateway, Y/N hears the Evil Entity contact him in his mind from the crystal sarcophagus.
Evil Entity: Soon! Soon I will be free! The time of the Nibiru is nearly at hand. The planets are coming into alignment, working toward my release, as are you and your friends, brother. Even though you know it not, I forged you. You are my proudest creation. So come now, brother of Nibiru. Be strong and set your brother free so that I may bathe this world in fire.
Y/N shakes his head as he drowns out his brother's voice and continues to walk with the gang.
The gang follows the original Mystery, Inc. through the caverns.
Brad: Judy, I have to say, this dark cave is doing wonders for your complexion.
Judy: Really? It's so nice of you to notice. Thank you, Brad.
Brad: You're welcome, Judy. In this light, I can barely see your multitude of wrinkles and your mouth full of decaying teeth.
Judy: That's it, Bradley!
Judy tackles Brad and fights him.
Professor Pericles: Stop it! You two are behaving like children.
The Kriegstaffebots pull Judy off as Judy kicks Brad.
Mr. E: The cursed treasure is tearing us apart. I wish Cassidy, F/N, and M/N were here to see you all go to pieces.
Professor Pericles: Oh, Ricky, you always lacked the stomach for greatness. Forward! Marschieren!
They continue to march forward as Judy and Brad stare at each other angrily. The gang sees them on the move.
Fred: They're on the move.
Y/N: Let's go.
They continue to follow as Shaggy pulls out his last hamburger.
Shaggy: Like, Scooby-Doo, old pal, this is it.
Scooby: The last hamburger.
Shaggy: We've already eaten all of our snacks. I was saving this for an emergency.
Scooby: This is an emergency. That's the last hamburger.
The two eat the hamburger.
Scooby: Looks like we're roughing it from here, Raggy.
The Original Mystery Incorporated reaches the first gate as they stop.
Professor Pericles: Beautiful.
Brad: I'm sorry to ask, Professor Pericles, but-
Judy: What are we waiting for?
Professor Pericles: The kinder. I know they are out there following us. Give them a minute. They will soon understand their part in all this. But they must hurry. The planets are nearly in full alignment. The time of Nibiru is almost at hand.
The gang all watches the group.
Shaggy: Like, dig those crazy symbols on those gigantico doors.
Y/N: The dream world.
Shaggy: The what world?
Velma: The dream world. The keys. Everything we saw, it finally makes sense.
Daphne: Professor Karen did say that the dream world would show us what we needed to find.
Fred: And it showed each of us the keys.
Velma: And what they were for.
Daphne: The fourth key is the element of air.
Scooby: The third key is the element of earth.
Shaggy: The second key is the element of water.
Velma: And the first key is the element of fire. Each one of the 4 keys opens a gate leading down. That first gate is covered in alchemy symbols for air.
Daphne: But if that's the first gate, why is it attached to the fourth key?
Fred: Because it's in reverse.
Shaggy: Of course it is. Like, why would any of this make sense?
Velma: It makes perfect sense, Shaggy. We're working outside in.
Velma lays out the keys.
Velma: This is the fourth gate. The next one will be the third. And then the second. And then ultimately the first.
Y/N: And then my brother.
The Original Mystery Incorporated continues to wait.
Professor Pericles: All right, you Mystery Incorporated. I know you're out there and you have the key.
Mr. E: Even if the Mystery Incorporated kids are out there, what makes you think you can make them do what you want?
Professor Pericles: Because, my dear Ricky, everyone has their weakness.
The robots open the box pulling out an unconscious Marcy.
Velma: Marcy! No!
Professor Pericles sees them.
Professor Pericles: Good kinder. Now come cooperate and I will not harm the Hot Dog Water.
Y/N: I'll do it. I'll go.
Daphne: No, we all go together. No splitting up. Never again.
The gang all walk down as Fred sees his real parents.
Fred: Mom, dad.
Brad and Judy: Son.
Professor Pericles: Ahh, the fourth key. I know you had found them. Here, allow my Kriegstaffebots to open the gate. It is very dangerous.
Y/N: I don't need your help, Pericles.
Professor Pericles: As you wish, L/N.
The gang walks up to the door and Fred stops Y/N.
Fred: If this gate is what I think it is, and I think it's a big fat trap, it might work in our favor. Hold on to something.
Everyone but Y/N all go separate ways as Professor Pericles notices them holding onto the rocks. Before Professor Pericles could do anything, Y/N pulls the lever and the Kriegstaffebots grabs Y/N only for the mouth on the door to open, causing it to begin sucking in air with tremendous force. As everyone struggles against the vortex, some of the Kriegstaffebots are destroyed by being sucked into the hole.
Professor Pericles: The redhead!
One of the surviving robots grabs Daphne and throws her towards the gate.
Y/N: Daphne! No!
This forces Y/N to disarm the trap by plugging the hole with the sailcloth as it glows green. This also serves to open the gate itself, revealing a strange dimension of floating islands and long wooden bridges. While Pericles is distracted by the events before them, Marcie takes him as a hostage.
Professor Pericles: What is the meaning of this? Put me down, you horrible girl.
Marcie: Not a chance, you nasty little monster. Move and the bird gets it.
The robots' approach as Marcie strangles the parrot.
Professor Pericles: Back off! No one move!
Marice turns to the gang.
Marcie: You guys go. Do what you have to do. I've been trapped in that box long enough to hear everything Professor Creepy Bird has in mind. Find that entity and destroy it. I'll hold them off as long as I can. Go. Now!
Velma: No, Marcy. I won't. I can't.
Marcie: You have to. The world needs you. Don't worry about me, V. I'll see you when this is over.
The gang leaves as the robot approaches as Marcie backs up.
Marcie: One more move and I pluck this ugly little chicken.
Marice begins to pull feathers from Professor Pericles.
Professor Pericles: Ow! Nein! Nein! Stop!
The robots stop.
Marice: Heh.
As the gang rushes through the gate, Marcie turns to Mr. E.
Marice: E, I guess I expected more from you.
Mr. E: So did I, little girl. So, did I.
Brad takes his belt off and gives it to Judy.
Brad: It's all in your hands now, Judy.
Judy uses her husband's belt as a whip to trip her up, freeing Pericles and leaving Marcie on the ground.
Marcie: Ow.
Brad: Silly child. We were springing impromptu traps before you were born.
Judy: That's right, Brad.
Brad: Thank you, Judy.
Marcie backs up as the Kriegstaffebots aim their gun at her. Within the air dimension, Scooby hears the distant sound of the robots' gatling guns. Scooby whines as Velma looks at him.
Velma: Come on, Scooby. We have to keep going.
Back in the cave, Mr. E looks at Professor Pericles.
Mr. E: You make me sick, Pericles. I wish I had never saved you all those years ago.
Professor Pericles: Hmm. Do I care? No.
Mr. E: Maybe you should care.
Professor Pericles: Perhaps you should care more about the poisonous cobra that I've implanted in your spine. Now let's move.
The group marches through the gate as Mr. E follows. The gang reaches the second gate.
Shaggy: Like, the second gate.
Fred: Somebody hand me the mortar bowl.
Shaggy: Like, Fred is really in his element here, huh?
Daphne: Pun intended.
Scooby hands Fred the bowl as it glows green.
Fred: Earth.
Fred uses the mortar bowl, and the door slightly opens.
Shaggy: Like, that was very anti-climactic.
Y/N: No kidding.
They then enter a mysterious cavern as something appears behind them. They turn and see a fierce rock monster.
Shaggy: Like, zoinks!
Scooby: Rock monster!
Daphne: Jeepers.
Y/N: Fred! We need a trap!
Fred: Let's see. Trap. Trap. I really don't have one handy. Maybe we should fall back on our old standard. Run!
Y/N grabs Daphne's hand as the six runs as the monster chases them trying to attack them as he launches Scooby and Shaggy as they continue to run. The monster throws rocks at them and continues the chase.
Shaggy: Faster!
Shaggy and Scooby get separated from the others as the rock monster continues to chase them. They climb up a cliff as the rock monster follows only to see they are gone and walks off. Shaggy and Scooby smile only for the rock monster to appear beside them and roar as the two run up a rock as the monster begins to destroy it. The rocks fall as Scooby and Shaggy fall to the ground and the rock monster rises from the debris and chases the two as the others reach a dead end.
Fred: Velma, what kind of rock is this behind us?
Velma: It's granite.
Shaggy and Scooby continue to run from the monster.
Y/N: Shaggy, Scooby, over here. Run this way!
Shaggy and Scooby run over towards them.
Fred: Wait... Wait for it. Wait. And... now!
Y/N tackles Scooby as Fred tackles Shaggy and they all jump out of the way as the beast runs into a granite wall.
Fred: Okay, that doesn't really count as a trap, but-
Shaggy: Works for me.
Scooby: Me, too.
The planets slowly continue to become in alignment.
They continue to walk as they see stairs leading to the third gate.
Daphne: The third gate.
Velma: And the second key. Water.
They approach the gate and Fred pulls out the helmet.
Fred: Looks like there's only one place to fill it up.
After using the conquistador's helmet to take water from the wall, the gate turns into a boat that sends the gang flying off a waterfall and into the open ocean.
Shaggy: Oh, no! No!
They fall into the open ocean drifting on the boat.
Y/N: Now, that was definitely a trap.
Shaggy: Like, dudes, where are we?
Daphne: And for that matter, where the heck have we been for the last two keys?
Velma: We're traveling through different dimensions. An intriguing feature of string theory and advanced physics is that it predicts extra dimensions. In classical string theory, the number of dimensions is not fixed by any consistency criterion.
Shaggy: What is she talking about?
Scooby: You're asking me?
Y/N: English please.
Velma: The Planispheric Disk not only maps 3-dimensional space, but the fourth dimension of time and beyond. Worlds between worlds.
Shaggy: Like, dude, that's all well and good-
Scooby: Even if we don't understand a word of it.
Shaggy: But, like, how are we gonna find the last gate?
Scooby: Yeah. All I see is water. Endless water.
Velma: Jinkies. Shaggy and Scooby are right.
Daphne: We're trapped in the middle of nowhere with no way out.
The Original Mystery Incorporated continues their journey as they pass through the earth dimension
Professor Pericles: Looks like the kinder are having fun, and they're all still alive.
Judy: That's our Fred.
Brad: A chip off the old block.
Judy: Blockhead, more like.
Brad: Thank you, Judy... Hey!
Mr. E: You're insane. All of you. None of us are going to make it out of this alive. None of us. And I'm glad.
Meanwhile, the gang were still drifting in the open ocean.
Shaggy: I can't take it! I can't take it!
Scooby: It's ok, Raggy.
Shaggy: No, Scoob, it is not okay. We're totally lost at sea. No wait. Correction. Lost on an interdimensional sea, alone and adrift between universes. Dudes, life is completely turned upside down.
Velma: Upside down. Shaggy Rogers, you're a genius.
Shaggy: Like... like, huh?
Velma: It's not up, it's down. The gate is down.
Y/N puts his head underwater and a glowing light.
Y/N: She's right.
The other look as well.
Daphne: Jeepers. You think the fourth gate is down there?
Fred: Only one way to find out. Come on, gang.
They all swim underwater and they emerge from a pool.
Scooby: Freaky.
daphne: Over there.
They see the last gate and go up to it.
Daphne: The last gate.
Fred: This is it. We made it, gang.
Velma: I don't like what's waiting for us beyond that door.
Scooby: Evil.
Shaggy: Pure evil. That we must destroy with the Heart of the Jaguar.
Scooby: Let's get this done.
Velma: Wait. If things prove to be bigger than us, I just want to tell you guys-
Daphne: No. Nothing is bigger than us. It's the six of us. We can do this together.
Shaggy: Here, let me do the honors.
Shaggy aims the flintlock and fires it only for the bullet to ricochet around the room.
Fred: I don't get it. The key didn't work.
Daphne: That's because the flintlock itself isn't the key. Look, it's the flint.
Fred: Daphne, you figured it out, you do the honors.
Daphne opens the gate by slotting it into an opening on the lock. The gang enters a lava-filled cavern.
Shaggy: This place is like mega creepy and scary. Is it too late to turn back?
Y/N: Yes. Way too late.
They continue as they come upon the Evil Entity's crystal prison. Y/N brings out the Heart of the Jaguar.
Y/N: So, what now?
Evil Entity: Open the sarcophagus, brother.
Shaggy: It-it spoke.
Evil Entity: Turn the lock. Set me free.
Fred: We aren't here to free you.
Y/N: We're here to destroy you.
Evil Entity: Destroy me? Never. You have no choice. This is your destiny, brother. Everything you have done, you have done for me. I brought you together as I brought all those together before you. I made you into friends. Forced you into a group. I am the author of your every hope and dream. All to this purpose you set me free, brother.
At that moment, the planets are aligned and Nibiru has begun.
Shaggy: Like, is-is this evil telling the truth? Like our whole life, our friendship has been a lie?
Fred: Maybe everything we think we know, none of it is real.
Daphne: No. I refuse to believe it. My love for Y/N is real. I know it. And I love you all. You're my best friends.
Velma: Daphne's right. Every word this thing spits out is a lie.
Velma looks at Y/N.
Velma: Destroy it.
Y/N: With pleasure. We'll never set you free, brother.
Y/N raises the spear.
Professor Pericles: That's too bad.
They see Professor Pericles, whose group has finally caught up with the gang.
Professor Pericles: Because I will.
Before Y/N can destroy the Evil Entity, Professor Pericles snatches the spear and throws it away. With the remaining Kriegstaffebots holding the gang at bay, Professor Pericles opens the sarcophagus, releasing the Evil Entity at last.
Evil Entity: The time of Nibiru has come.
The Evil Entity is released as it takes its original form, a floating mass of dark green tentacles forming sharp teeth, with two glowing yellow eyes with green sclera. The Evil Entity laughs as everyone looks at it.