This is how Primus vs Unicron goes in To Cybertron and Back Again.
[Unicron tries to grab the Dark Spark from Starlight, Trixie, Thorax, and Discord, but Primus punches him away.]
Primus: This ends here.
Unicron: I was wondering if you were ever going to come, brother.
Primus: Unicron, I have been waiting for this day to come.
Unicron: The Dark Spark belongs to me.
Primus: Let's finish this, brother. Once and for all.
Unicron: I was just about to say the same thing, brother.
Primus: One shall stand.
Unicron: One shall fall.
[Primus and Unicron fight in a battle between brothers while Starlight, Trixie, Thorax, and Discord watch]
Starlight Glimmer: Yeah!
Trixie: Go on!
Thorax: Give him the wack!
Discord: Come on!
[Unicron begins to gain the upper hand on Primus]
Unicron: Equines and Cybertronians don't deserve to live.
Primus: They deserve to choose for themselves, brother.
Unicron: Then you will die with them, brother.
Starlight Glimmer: Go!
Thorax: Go on, Primus!
Discord: Don't let him beat you!
[Primus then summons the power of the Elements of Harmony and begins to gain the upper hand on Unicron.]
Primus: This is how it started, brother, this is how it ends.
Unicron: You were always the Cybertronians' favorite, brother.
[Primus punches Unicron into a wall and Unicron's optics flash out. Primus believes that he had destroyed Unicron, Starlight, Trixie, Thorax, and Discord hand the Dark Spark to Primus, but Unicron jumps into the air with his flail, making one last attempt at nailing Primus. Primus catches the flail in its path and yanks Unicron towards him, shoving the Dark Spark into his chest, killing him.]
Primus: You left me no choice, brother.
Starlight Glimmer: You were awesome!
Trixie: I agree.
Thorax: Me too.
Discord: That was amazing.
Primus: Starlight Glimmer.