Here's how confronting the Nightmare Family and Brian's betrayal goes in Revenge of the Nightmare Family & Changling Queen.
[we now view Brian out in a dark part of the city in an alley, as he's thinking about what Nightmare Moon and Sombra said]
Nightmare Moon: (in Brian's mind) Yes. We understand your feelings, especially for Sylveon.
King Sombra: (in Brian's mind) I can feel your anger, Brian. It gives you focus, makes your stronger, and makes you more attached to Sylveon.
Queen Chrysalis: (in Brian's mind) We can help you out with your own problems, and to protect the one you truley love
[Brian then races out of the alley and then hops in a shuttle and he then takes off for Canterlot Castle]
[Then, in one part of Canterlot Castle, Gleaming Sheild and 3 other royal guards are searching for Brian, but then Gleaming Shield senses something]
Gleaming Shield: You 3, come with me!
[the 4 guards race down a hall and come to a conference room with a big window, and there, as the conference desk, is none other than Nightmare Moon And King Sombra]
Nightmare Moon: Well, well. Looks who's here.
King Sombra: Come to see Equestria's new rulers?
Gleaming Shield: In your dreams!
Nightmare Moon: So, what can we do for you?
Gleaming Shield: In the name of the Equestrian Republic and all Jedi; (he and the guards draw and ignite their sabers) You 2 are under arrest.
King Sombra: Are you threatening us?
Gleaming Shield: The Royal Court will decide your fate.
King Sombra: (snarling) We are the Royal Court.
Gleaming Shield: Not yet, you aren't!
Nightmare Moon: [Force deploys one of her Sabers] It's treason then. (ignites her Lightsaber)
King Sombra: [draws and ignites his Darksaber]
[they both Force leap foward and roars as they clash sabers, as Nightmare Moon kills one of the others guards, and Sombra does the same, as they fight against Gleaming Shield and the other guard bout soon, the other guard is killed and Gleaming Shield is left to fight them]
[they furiously clash sabers and soon are heading cloaser to the big window]
[Just then, Brian's shuttle lands on a landing pad and Brian races into the castle]
[back to the duel, Nightmare Moon, Sombra, and Gleaming Shield are still fighting and then they smash the window open as they clash sabers again, and come into a blade lock, but then Gleaming Shield Force kicks the 2 back, making them drop their sabers and then corners them, just as Brian walks in]
Gleaming Shield: You 2 are under arrest, Dark Lords.
Nightmare Moon: Brian, you arrived just in time!
King Sombra: You see what's going on? The Jedi are taking over!
Gleaming Shield: The Sith will not return and destroy the Republican or the Jedi again! You have lost.
Nightmare Moon: No. No. NO, YOU HAVE LOST!!! [she then fires Force Lightning at Gleaming Shield]
[But Gleaming Shield blocks it with his saber]
King Sombra: He's a traitor!
Gleaming Shield: They are the traitors!
King Sombra: We have the power to protect the ones you love! You must choose!
Gleaming Shield: Don't listen to them, Brian!
Nightmare Moon: Don't let him kill us! [soon Nightmare Moon is losing her strength] I can't hold him any longer. I can't. I can't. I'm too weak. Brian! (stops Force Lightning) Brian! Brian, help us!
Gleaming Shield: I'm going to end this madness, once and for all!
Brian: You can't, they must stand trail.
Gleaming Shield: These 2 are the bringers of Darkness and Nightmares, they're too dangerous to be left alive!
Nightmare Moon: I can't hold back. (weakly) Please. Don't kill us!
Brian: It's not the Jedi way!
King Sombra: Please don't!
Brian: They must live, I need them!
Gleaming Shield: [thinks for a moment] No, I won't let them take control! [he then brings back his saber]
Nightmare Moon: No, please, DON'T!!
Brian: (as Anakin) NOOOOOO!!!!! [he then ignites his Lightsaber and cuts off Gleamign Shield's arm at the last second!]
Gleaming Shield: AAAAHH!!!!! AAAAHHH!!!! WHAT ARE YOU DOING?!
King Sombra: YES!!! [he then fires Force Lightning at Gleaming Shield]
Nightmare Moon: (in Royal Canterlot voice) UNLIMITED POWER!!! [she then joins in firing Force Lightning at Gleaming Shield and then he's thrown out the window and down to his doom]
Brian: [extinguises the blade of his Saber and stares in shock] WHAT HAVE I DONE?! [he then walks backward and drops his saber]
King Sombra; [gets up] You're forefilling your destiny, Brian.
[then Nightmare Hiro walks in]
Brian: Who is that?
Nightmare Moon: This, is my apprentice, Nightmare Hiro.
King Sombra: Become my apprentice. Learn to use the Darkside of the Force.
Brian: [panting] I will do what ever you want.
King Sombra: Good.
Brian: Just help me protect Sylveon, and the Eeveelution kids. I can't live wthout them.
King Sombra: To prevent death, is a power only one has accheived. But if we all work together, we can discover it.
Brian: I pledge myself to your teachings.
King Sombra: Good.
Nightmare Moon: The Force is strong with you. A lot stronger than your so-called "friends". A powerful Sith, you will become.
King Sombra: From this moment on, you will be known as: "Darth.. Manacore."
Brian: Yes, my Master.
[elseway, Zecora senses Brian turning to the Darkside]
[back in the conference room]
King Sombra: Celestia didn't put you back in charge, because they fully don't understand you, nor do the others. They think you're nobody.
Nightmare Moon: So, you're the only Jedi who doesn't know their plot.
Brian: I argee. If they find out about this, they'll destroy us.
Nightmare Moon: Every single Jedi, including your friends, and all their allies are now enemies. We must destroy them all.
Brian: I understand.
King Sombra: We must move quickly, if we don't stop them, we'll be destroyed.
Nightmare Moon: First, we want you to go through the whole place. And kill all the Jedi within here. This is catch them off guard.
Brian: What about the other Jedi all across the galaxy?
King Sombra: They will be delt with.
Nightmare Moon: After you finish that task, come to us for your next instruction.
Brian: As you wish.
King Sombra: Do what must be done. Only then, you will be strong enough in the Darkside, to protect your family.
Nightmare Moon: Even if you have to use your firearms, as well as your saber.
Brian: I accept. [he then leaves]
King Sombra: Now, the purge of all Jedi shall began.
[we now come to a another spot in Equestria, where we see Queen Chrysalis and Discord!]
[then Nightmare Moon appears on a hologram]
Nightmare Moon: Queren Chrysalis. Discrod. The time has come. It's time to exacute, Order CH-55.
Queen Chrysalis: Consider it, exacuted. (hologram shuts off) [to the Changling Army] Changlings, it's time for Order CH-55!
Discord: Now, go out and do what must be done!
[all Changlings set off at once.]