This is how the Lightsaber duel goes in Night Furies vs. The Nightmare Family Part 2.
[They clash their sabers as "Duel of the Fates" starts playing (Luna takes on Nightmare Moon while Yuna does Sombra)]
King Sombra: [cackles] You really think a young foal like you can take me on?
[The 4 continue clashing their lightsabers as they come onto of one the outside balconies]
Nightmare Moon: I must say, your lightsaber skills are fantastic, Master Yoda taught you will.
Princess Luna: Well, I've only just begun! [clashes lightsaber]
[Then Sombra clashes his Dark saber against Yuna's as Yuna strain to hold it back]
King Sombra: Now, you will see, that Darkness can win!
Princess Luna: Yuna!
King Sombra: It's gonna take more than Vikings to Stop me or Nightmare Moon! And now you'll get yours!
Princess Luna: [force pushes Nightmare Moon asside and then drives her lightsaber in King Sombra's back]
King Sombra: Ah!
Princess Luna: [shuts off her Lightsaber and then Force throws Sombra's body over the side] Not while I'm still stnding!
[But then Nightmare Moon bucks Luna over the balcony]
Princess Luna: Aaah!!
[Luna then lands in the castle courtyard below as Yuna jumps down to her]
Princess Luna: [groans]
Yuna: [listens for a heart beat and still hears one] Thank goodness.
Nightmare Moon: [cackles] You little foal! You really think you could defeat me?! Your own mother couldn't even defeat me! Now, we shall finish this once and for all! [jumps down]
[As Nightmare Moon jumps down Yuna reactivates her Lightsaber and then draws the Lunar Saber at the same time]
Nightmare Moon: So, you have the Lunar Saber? Oh, how I've been searching for that saber for years! Once, I finish you, that Sbaer will be mine! [reactivates her own lightsabers]
[Yuna then charges forward and they clash their sabers]
[The 2 continue clashing their Sabers at different angles until then down one more clash and strain against each other]
Nightmare Moon: Is this how you want to die? [she then uses her magic to throw Yuna up and then she throws her against the wall]
Yuna: [groans] Have mercy! Please! PLEASE!!
Nightmare Moon: There is no mercy. [she then Force lightning zaps her!]
Princess Luna: Yuna! Stop it! Stop it!
Nightmare Moon: This will teach you to banish us to Titan! [continues zapping Yuna]
Yuna; [yelling in pain]
[Just then a roar is heard as Toothless just from the balcony]
Toothless: ROAR!!!! [he then jumps onto Nightmare Moon and then throws her at the wall]
[Then Nightstar jumps down and smacks Nightmare Moon with her tale]
Nightmare Moon: WHAT?! NIGHT FURIES?!
[She then tries to grab her lightsabers but Toothless blast her with a plasma blast]
Nightmare Moon: Uh!
[Then Nightstars fires a plasma blast]
Nightmare Moon: Gah!
Hiccup: Now, you'll pay for haunting me and Yuna! [he jumps down]
Nightmare Moon: No! [she then shoves Hiccup asside]
Hiccup: Oh no! [grabs on a root on the side of the cliff]
Nightmare Moon: [cackles] Not even a scrawny Viking can stop me now!
Hiccup: [he then starts to focus his concentration really hard]
[And then the Lunar Saber shifts a little]
Princess Luna: Huh?
[Then Hiccup jumps up and uses the Force to grab the Lunar Saber and he activates it]
Nightmare Moon: WHAT!?
Hiccup: YAAAAAHHH!!! [lands and then slices Nightmare Moon]
Nightmare Moon: UH!!
Hiccup: Okay, you 2, send this demon over the side!
[Toothless and Nightstar both fire a plasma blast, which sends Nightmare Moon over the side of the cliff]
Nightmare Moon: NOOOOOOOOOOOOOOOOOOOOOOO!!!!!!!!!!!!!!!!!!!!!
[She then plumments down the cliff, revealing her split body]
Yuna: [looks over the side] They're gone!
[Then Astrid jumps down and helps Luna up]
Astird: You are alright?
Princess Luna; Yes, I'm fine.
Hiccup: [deactivates the Lunar Saber] Okay, I have offically gained a new respect for these light swords. [gives it back to Yuna]
Astrid: Come here, you. [kisses him]
Yuna: You alright, Mama?
Princess Luna: Yes. Come here.
[then Nightstar comes up and nuzzles Yuna]
Yuna: It's okay, girl. I'm fine. Thanks to you, Toothless, and Hiccup.
Astrid: Okay, if you ever find the time. You totally should teach us more about those light swords.
Princess Luna: Sure, we'll try to find time to....
[Then Princess Luna starts groaning]
Hiccup: Princess! What's wrong?
Princess Luna: Hiro! Tia! She's coming!
Princess Celestia: The foal?
Princess Luna: Yes!
Hiro: Celestia, put her in my cab!
Hiccup: Come on, Bud! [hops on Toothless]
Astrid: [whistles] Stormfly!
Yuna: Let's go girl! [hops on Nightstar]
[Stormfly then flys down and Astrid hops on]
Hiro: To Canterlot!
[they all race to Canterlot]