A Monster in Canterlot/Transcript

Opening
Theme song)

(A title card “Guest staring: The Mane 6”)

Shaggy (voice): Today we meet Twilight and her friends.

New Royale City is dominated
(The Mystery Inc sees New Royale City's been dominated and deserted, everyone are missing after Lorcan's funeral)

Daphne: What happened here?

Velma: I don't know. It's probably been... destroyed.

Fred: I don't get it, first this place is amazing and now it's in destruction, i mean we're here to visit, Cillian and Lilly.

The Execution Demon appeared
Rainbow Dash: Hello?! Is anypony or anyone in the barrel?

Shaggy: Nobody in here, but us chickens.

Fluttershy: That's right. Oh, this is why i missed Lorcan.

Rainbow Dash: Same here.

Shaggy: Wait, you know Lorcan?

Velma discovers the girl's soul
(Velma hears something and walked into a room)

Twilight Sparkle: Uh, Velma, i wouldn't go in there if i were you.

Velma: Why?

Spike: Why not, Twilight?

Twilight Sparkle: That room where all the souls are.

Velma: Let's see them.

(Velma opens the door. All of the souls are missing, All except one)

Shaggy: They're gone. They really are.

Fluttershy: Oh my. Look.

A Girl:  I don’t recognize you. You are new. I remember this... scenario however. It’s a strange thing to want to do, to come here. I’m curious what events would lead a person to want to spend their nights in a place like this... willingly. Maybe curiosity, maybe ignorance... There is a space under my room. I recommend that you hurry though. You will be safe there, just try not to make eye contact... it will be over soon. Celestia will lose interest.

Twilight Sparkle: She's right. Hide!

(Velma, Shaggy, Scooby, Twilight and Fluttershy hides from Celestia until the coast is clear)

A Girl:  When your dragon comes back, he is going to tell you that he was unsuccessful, that you must free me. Can you help me?

Twilight Sparkle: Don't worry. I will help.

A Girl: Good, Spike will then tell you to go back to New Royale City. If you follow my instructions, i will die. Your friend, Lorcan will not be able to coming back in this dimension anymore. He will miss you, Mystery Inc. The power will be restored shortly. When you return to the city, go rescue Daphne and Fred. Celestia and the Execution Demon cannot see you and can only listen for our conversation. When you hear my music become louder, i will warn you to freeze, listening for you. Wait, and be still.

(The girl disappears)

Shaggy: Wait... Lorcan is still alive?

Twilight Sparkle: You didn't know? He's gone home to his dimension to be with his family.

Fluttershy: Yeah, he was dying but once when we found Lorcan in the forest, we helped him get home.

Velma: We better tell the others.

Twilight Sparkle: Right there's no time to lose.

(They head back until The Execution Demon appears)

Shaggy: Zoinks! Like run!

(Shaggy, Scooby, and Fluttershy run the other way as the demons chases them)

Shaggy: Faster, faster! Like, he's gaining on us!

(They continue running)

Cillian and Lilly to the rescue
(The Mystery Inc are in the dead end with the Mane 6 while Celestia and the Execution Demon got them)

Princess Celestia:  This is where it ends. Surrender now.

Shaggy: Hohoho! Like, I'm too young to be executed!

The Execution Demon: Prepare to meet your doom!

(Just then, Cillian and Lilly appeared in between of the Mystery Inc, Mane 6 and Celestia)

Cillian: Shaggy, Scooby! Don't worry!

Princess Celestia: You again! You will be executed!

Lilly: It's over, Celestia and there's nothing you can do to stop us!

Princess Celestia: Get them!

(The Guards start fighting Cillian and Lilly)

Twilight unmasked The Execution Demon
(The Execution Demon is caught and Twilight unmasked him)

Twilight Sparkle and Lilly: Prince Blueblood?

Cillian: The first Guardian of the Gate during Lorcan's part of our story?

Prince Blueblood: That's right!

Rarity: But why?!

Ending
TBA