This is how Orion Pax and Nightfall Twinkle become Decepticons goes in episode 1 of season 2 of Ryan F-Freeman's Adventures of Transformers: Prime.
Optimus Prime: (voice) Previously on Ryan F-Freeman's Adventures of Transformers: Prime.
Megatron: Orion Pax and Nightfall Twinkle are one of us.
[end of recap]
Ratchet: When Optimus used the Matrix of Leadership and Twilight used her Magic of the Alicorn, they not only lost the wisdom of the Primes and Alicorns. They lost themselves. They have reverted to their old names, Orion Pax and Nightfall Twinkle.
Rainbow Dash: No way!
Pinkie Pie: Seriously?
Applejack: They think they're Cons?
Fluttershy: Oh my.
Starlight Glimmer: [gasps]
Arcee: And Thomas is missing.
Arcee: Don't know. He was there with us at the Earth's core.
Princess Celestia: There is only one thing Thomas would disappear for.
Princess Luna: And that is to go to the Nemesis.
Princess Cadance: And rescue Optimus and Twilight.
Megatron: Attention, crew. Our guests are currently in isolation, to help ease their transitions. But when Orion Pax and Nightfall Twinkle emerge, they are to be shown every courtesy. And the first to adress them as Optimus Prime or Princess Twilight will have their voice box ripped out.
Airachnid: Lord Megatron, is it wise to allow an Autobot and Princess, current or former, take full run of the Nemesis?
Megatron: Oh, Nightfall and Orion will indeed earn their stripes.
Knock Out: Welcome back to the winning team.
[Megatron, Orion Pax, and Nightfall Twinkle walk into the bridge and Vehicons look at them]
Megatron: You two have been captives of the Autobots and have been locked in stasis for quite some time, Orion and Nightfall. Long enough for us to gain exodus on another world.
Orion Pax: Exodus?
Nightfall Twinkle: Why?
Megatron: Because the warlord Ratchet's and deadly friendship Princess Cadance's careless actions lead to this.
Orion Pax: [gasp] Cybertron.
Nightfall Twinkle: Equestria. I can't believe Ratchet and Cadance capable of such horrors.
Megatron: Yes. And to think their mad quest for power continues their marauders pursued us to this planet's orbit. We feel its species are not ready to behold us. But we have resolved to protect this world from the same tragedy which was dealt to our own.
Orion Pax: One question, Megatron.
Nightfall Twinkle: Why are we called Decepticons?
Megatron: Another craven Autobot scare tactic. The name was meant to demonize us. Instead, we wear it as a badge of honor, for if speaking the truth is deception, then we are gladly guilty.
Orion Pax: [nods]
Nightfall Twinkle: [nods]
Megatron: There will be time for catching up. You two need to rest.
Orion Pax: Megatron! We will do our part to stop Ratchet and Cadance's unspeakable crimes of aggression.
Nightfall Twinkle: This I vow. With all Orion's Spark and my heart.