This is how Twilight vs. Thunderwing and Unicron tortures Twilight goes in The Return of Unicron.
Thunderwing: You cannot hide forever, Twilight.
Twilight Sparkle: Yes, I can.
Thunderwing: Give yourself to Unicron's side. It is the only way you can save your friends. Yes, your thoughts betray you. Your feelings for them are strong. Especially for your... Sister-in-law. So...you have a sister-in-law. Your feelings have now betrayed her, too. If you will not turn to Unicron's side, then perhaps she will.
Twilight Sparkle: Never!
[Twilight and Thunderwing battle, ending with Twilight blasting off Thunderwing's right hand]
Unicron: Good. Your hate has made you powerful. Now, fulfill your destiny and take Thunderwing's place at my side.
Princess Celestia: You can't make her.
Princess Luna: She won't do it.
Princess Cadance: And never will.
[Twilight looks at her horn, Dark Magic at ready, and Thunderwing's severed hand]
Twilight Sparkle: Never. I'll never turn to your side. You've failed, Lord of Chaos. I am a Princess.
Unicron: So be it...Princess. If you will not be turned, you will be destroyed.
[Unicron shoots lightning from his hands at Twilight. Twilight falls down in pain as Thunderwing gets up and walks to his master's side]
Unicron: Young fool... only now, at the end, do you understand.
[Unicron shoots lightning at Twilight twice]
Unicron: Your feeble skills are no match for the power of chaos. You have paid the price for your lack of vision.
[Unicron shoots lightning at Twilight as she writhes on the floor in unbearable pain as Thunderwing watches and Princess Celestia, Princess Luna, and Princess Cadence watch in horror]
Unicron: Now, Princess Twilight...you will die.
[Unicron increases his lightning in intensity and shoots at Twilight as she writhes in pain.]
Princess Celestia: Twilight!
Princess Luna: This is not good!
Princess Cadance: No!
[Thunderwing looks at Princess Celestia, Princess Luna, and Princess Cadance]