This is how Unicron's defeat goes in The Crystalling.
[Unicron's eyes appear]
Unicron: At last! The Crystal Empire will be mine!
[Unicron laughs evilly as Dark Energon crystals start to pop out of the ground]
Princess Celestia: Twilight, you must listen to us!
Princess Luna: You have to stop this!
Unicron: Twilight may hear you, but she can't help you.
[Twilight is screaming in pain]
Unicron: For she is enduring eternal suffering.
[Twilight gets a headache while a superimposed image of Unicron flashes over her.]
Unicron: Twilight, destroy the Princesses of the Sun and Moon. I command you!
[Twilight's eyes turn purple as she walks over to Princess Celestia and Princess Luna and readies her magic]
Princess Celestia: Twilight! Don't!
Princess Luna: You have to be stronger than he is!
[Twilight tries to fight it off]
Twilight Sparkle: I am commanded by no one! Not that there's a fifth Alicorn.
[Unicron fires lightning at Twilight]
Unicron: How dare you disobey me?! You belong to me!
Princess Celestia: Don't listen to him, Twilight!
Princess Luna: You are in charge!
[Twilight looks at Flurry Heart, who is cooing encouragement]
Twilight Sparkle: No...! I am not Midnight Sparkle! I... am... PRINCESS TWILIGHT SPARKLE!! And the one magic I carry in me is... the magic of FRIENDSHIP!!
[Twilight powers up her magic.]
Unicron: You cannot defeat me, Princess of Friendship. I have transcended physical being. By my will alone, all upon this world shall fall into real chaos.
Twilight Sparkle: Not while Friendship and I still exist, Unicron. The Magic of the Alicorn will light our darkest hour!
[Unicron is hit by Twilight's powerful magic beam]