Here is how Princess Yuna and her friends discovered the Goosebumps Monsters attack in Welcome to HorrorLand.
However, Yuna and her friends found themselves in Fever Swamp.
Princess Skyla: This is so scary, I'm so scared.
Prince Sunlight: Oh, brother.
Jack Skellington: Don't you worry, Skyla. We will get you home safely soon enough.
Princess Yuna: Yeah, it's just a swamp filled with incredible creatures.
Emerald: What kind of swamp is this?
Princess Susan: Good thing that we wear boots for the swamp.
Prince Joshua: Let's keep moving.
Sonic the Hedgehog: Quick, this way!
Unknown to the group, Shaggedy was spying on them.
April: So, where are we?
Pacifica Northwest: (looking at the map) Fever Swamp.
Dipper Pines: Why is it called Fever Swamp?
Mabel Pines: Maybe someone has a fever? (rimshot)
Just as everyone looked at Mabel, Jack only facepalm himself.
Portal Glow: This isn't a joke, Mabel.
Honker Muddlefoot: It's actually a high fever that people go insane in this swamp and never get out.
Robotgirl: Really?
Princess Yuna: Are you sure, Honker?
Honker Muddlefoot: Maybe, but since Jack is with us, I'm pretty sure we'll be getting back to Ponyville.
With enough info, Shaggedy went off to warn Slappy, Bill Cipher, Grogar and Dr. Eggman.
Deep in Fever Swamp, Jack was making sure he kept Yuna and her friends together.
Jack Skellington: Stay close, Little friends. We'll be out of the swamp soon.
Princess Skyla: (hearing something) Hey. Do you hear that?
Just as everyone and everypony else heard what she heard, they were ambushed by a huge army of Goosebumps Monsters ready to attack them.
Apple Bloom (Human): What are those!
Princess Yuna: Goosebumps Monsters!
Princess Susan: Well, this is for us!
Suddenly, help came from Solarna leading the rescue party.
Princess Solarna: Back off! (as she'd blasts some magic at a couple of mannequins)
Jonny Quest: Hold on, Yuna!
Princess Yuna: Solarna! Jonny! K.I.T.T.! Bandit! Jessie! Hadji! Ben! Gwen! Kevin! Rook!
Bandit: (barking)
Snowdrop: They're here?
K.I.T.T.: Glad to be of any assistance!
Princess Solarna: We figured you'd be trapped, Little Sis.
Princess Sharon: We came as soon as we could.
Terramar (Human): Are we glad to see you guys.
Princess Yuna: What took you all so long?
Cosmo the Seedrian: Where were you?
Princess Solarna: Chancellor Neighsay sends in a rescue party to help.
Galaxina: Watch out! (as Will Blake is about to attack)
Hadji: Sim Sim Salabim! (using his mental powers to wrap him in chain)
Princess Yuna: I wonder if I could help him control his werewolf farm.
Ben Tennyson: Be careful, Yuna.
With one amount of her magic, Yuna used her beam to hep Will gain control of his werewolf form.
Will Blake: What happened?
Hadji: It is all right, Will Blake, you are among friends.
Gwen Tennyson: Yuna cured you with her magic to help you control your werewolf form.
Will Blake: I owe you one, Yuna, thanks.
Princess Yuna: No problem, Will.
Jonny Quest: Come on, let's get you guys out of here.
Princess Yuna: Thanks for coming for us, Big Sis.
Princess Solarna: Anything for you, Yuna.
K.I.T.T.: My scanner is picking up another way out.
Princess Yuna: Lead the way, K.I.T.T.
And so, Yuna and her friends had to keep going where K.I.T.T. is leading.