This is how Twilight vs. Thunderwing goes in A Canterlot Wedding.
[Twilight looks at the defeated body of Midnight]
Thunderwing: Yes. Kill him. He was weak, broken. Kill him and you can take your rightful place at my side.
Shining Armor: No!
[Shining Armor goes to stop Thunderwing from persuading his sister to kill Midnight but is knocked aside by the Unicron follower and Thunderwing blasts him with lightning]
Princess Cadance: [to Twilight] Help him!
[Twilight looks at Thunderwing blasting Shining Armor with lightning then looks at Midnight getting back up and ready to fight. Twilight tries to think what she should do.]
Twilight Sparkle: I don't know which activity to do first.
[Twilight looks at her brother and at Midnight and decides to help her brother]
Thunderwing: I can feel it in you. I can feel the dakness.
[Twilight then taps into the dark side]
Thunderwing: Yes. That's it. Use your anger, use your pain. Let it fill you, fuel you.
[Twilight lets the the dark side fuel her and give her all the strength she needs to defeat Thunderwing]
Thunderwing: Use your anger. Embrace the darkness.
[Twilight uses her anger to attack Thunderwing]
Thunderwing: Give in to it.
[Twilight ignores him as she continues to use the dark side powers to overpower Thunderwing]
Thunderwing: Join the dark side.
[Twilight ignores him as she fires a beam at Thunderwing, who fires a beam from his mouth]
Thunderwing: Feel it course through your veins.
[Twilight's beam overpowers Thunderwing's beam, causing him to fall. Twilight then runs up to him and uses her horn to strike at Thunderwing's head, but Thunderwing blocks it with his right arm and Twilight continues to strike his right arm]
Thunderwing: Keep striking at me.
[Twilight listens and keeps striking at Thunderwing's right arm]
Thunderwing: Surrender to it.
[Twilight ignores him as she keeps striking at Thunderwing's right arm]
[Twilight continues striking at Thunderwing's right arm]
Thunderwing: Yes. That's it.
[Twilight strikes at Thunderwing's right arm one last time then uses her magic to lift him up and drop him on the floor. Thunderwing looks at Twilight, who is angrily looking at him]
Thunderwing: What are you waiting for, Twilight? Finish me.
[Twilight prepares to when Princess Celestia puts a hoof on her shoulder]
Princess Celestia: He's beaten. Let it go.
Twilight Sparkle: It's a trick. He's stronger than you know and he must die.
Princess Celestia: Maybe so, but if you strike him down in anger, you'll end up back where you started.
Twilight Sparkle: Fine.