This is how Unicron arrives at the Crystal Empire goes in The Crystalling.
[At the Crystal Empire]
Princess Cadance: Did you hear that?
Shining Armor: Yeah.
[They see something in the distance]
Princess Celestia: No.
Princess Luna: It can't be.
[Midnight Sparkle flies into view]
Midnight Sparkle: Princess Cadance and Shining Armor, prepare to be obliterated.
Princess Cadance: Twilight?