This is how Thunderwing turns Twilight against her friends goes in The Return of Thunderwing.
[Twilight gets separated from her friends and hears a voice]
Twilight Sparkle: Thunderwing!
[Thunderwing lands and furls his wings]
Thunderwing: Twilight, you must accept my friendship.
Twilight Sparkle: Why?
Thunderwing: Because I can help you fix what happened in the past, like when no one believed you when you said that the fake Cadance was evil.
Twilight Sparkle: How do you know that?
Thunderwing: I saw what happened when you started saying she was evil, that she was Queen Chrysalis in disguise.
Twilight Sparkle: Seriously?
Thunderwing: Allow me to show you the worst mistake your friends made.
[Thunderwing shows Twilight the flashback when no one believed her about the fake Cadance being evil]
Twilight Sparkle: Oh.
Thunderwing: Things like that can be prevented if you join me. The choice is yours.
[Twilight's eyes turn red]
Twilight Sparkle: Okay. I accept.
[Meanwhile with Rainbow Dash, Pinkie Pie, Rarity, Applejack, Fluttershy, Starlight, Trixie, Thorax, and Discord]
Rainbow Dash: Do you think Bumblebee may be right, girls?
Pinkie Pie: Maybe.
Rarity: What do you mean "Maybe"?
Applejack: Bee may be young, Rarity, but he knows what he's seen.
Fluttershy: Yeah. He's actually really nice.
Starlight Glimmer: But what he's saying is true.
Trixie: I agree.
Thorax: Me too.
Discord: But Bumblebee can't be right all the time.
[They hear a noise and see Twilight helping Thunderwing find Dark Energon]
Twilight Sparkle: Thunderwing, look what I found.
Thunderwing: Dark Energon. Excellent.
[Rainbow Dash, Pinkie Pie, Rarity, Applejack, Fluttershy, Starlight Glimmer, Trixie, Thorax, and Discord arrive]
Rainbow Dash: Twilight!
Pinkie Pie: What?!
Rarity: Darling, what are you doing?!
Fluttershy: Uhm, Twilight?
Starlight Glimmer: Get away from Thunderwing!
Trixie: He's dangerous!
Thunderwing: Well Twilight looks like your former friends want you to get away from me.
Thunderwing: Your friend belongs to me now.
Rainbow Dash, Pinkie Pie, Rarity, Applejack, and Fluttershy: [together] What?!
Twilight Sparkle: Thunderwing is my only friend.
Thunderwing: Yes. Indeed I am, Twilight.
Starlight Glimmer: What did you do to Twilight?!
Trixie: We demand to know.
Thorax: Tell us, you monster!
Thunderwing: Show them your cutie mark, Twilight.
[Twilight then shows her former friends her new cutie mark: the purple symbol of Unicron]
Rainbow Dash, Pinkie Pie, Rarity, Applejack, and Fluttershy: (together) What?!
Starlight Glimmer: Unicron?!
Thorax: But he's defeated!
Discord: How did it get there?
Thunderwing: That is the symbol of Unicron the Destroyer.
Twilight Sparkle: Yes. And he will prevail.
Thunderwing: And we won't let you stop him.
Twilight Sparkle: Not this time.
Thunderwing: Come, Twilight. Let's find more Dark Energon.
Twilight Sparkle: Yes.
[Twilight and Thunderwing unfurl their wings and they fly away]
Rainbow Dash: Twilight!
Pinkie Pie: Oh no!
Rarity: What now?!
Applejack: We have to tell the Bots!
Starlight Glimmer: I agree!
Trixie: Come on!
Thorax: Let's go!
[The gang hurries off]
Optimus Prime: Thunderwing turned Twilight against you?
Starlight Glimmer: Yes.
Optimus Prime: How?
Starlight Glimmer: We don't know.