This is how Thunderwing and Pythor arrive at Canterlot and Thunderwing imprisons the Princesses goes in My Little Pony Transformers Prime: Optimus' Kingdom.
[Pythor and Thunderwing arrive at Canterlot only to run into Shining Armor and the Royal Guard]
Pythor P. Chumsworth: Shining Armor, why, whatever are you doing here?
Shining Armor: Back off, traitor.
Thunderwing: The only one Pythor betrayed was himself. [drains the guards of their magic] Abandoning his true nature to make friends with weak-minded equines who offer him nothing!
[Shining shoots a beam of magic at Thunderwing, who catches it in his core]
Thunderwing: [laughs then drains Shining's magic into his core]
Shining Armor: [weakly] How... could you... do this...?
Thunderwing: Why don't we go and have a little fun? I won't stand in your way.
Pythor P. Chumsworth: [giggles]
[Celestia, Luna, Cadance, and Twilight lay weak in the throne room when they hear Thunderwing coming. Thunderwing rips the doors off their hinges and tosses them aside as he and Pythor approach the princesses. Thunderwing decides to start with Celestia and opens his core to drain her magic as Pythor surprisingly turns his head away in shame. Thunderwing waits for Celestia's magic to come out, but nothing happens]
Thunderwing: What have you done?!
[Celestia remains silent. Thunderwing tries to suck out Luna, Cadance, and Twilight's magic, but they come with the same result]
Thunderwing: Where is your magic?!
[Thunderwing looks confused]
Thunderwing: Getting rid of your magic so that I cannot take it from you? That was your plan?
[Celestia, Luna, Cadance, and Twilight nod]
Thunderwing: How does it feel, knowing that soon, every Pegasus, Unicorn, and Earth Pony will bow to my will, and that there is nothing you can do to stop it?
Princess Celestia: You will not prevail, Thunderwing.
Thunderwing: Give my regards to Primus.
[Thunderwing creates cages out of Dark Energon and imprisons the princesses in them]
Pythor P. Chumsworth: You meant our will, didn't you?
Thunderwing: Of course. Here, I want you to have something. This was given to me by someone very close to me. I give it to you as a sign of my gratitude and loyalty.
Pythor P. Chumsworth: Oh, my! I do love a good accessory. I suppose that's Rarity and Bumblebee's influence.
[Pythor shows Thunderwing a glass window of them defeating him]
Thunderwings: [laughs] Amusing. But we have no time for such things. With the princesses as our prisoners, we can now– [looks and sees a stained glass window with Optimus' picture on it] Is this meant to be humorous?!
Pythor P. Chumsworth: Oh, no, I haven't touched that one yet.
Thunderwing: There's a prince? And you did not tell me this?!
Pythor P. Chumsworth: I just needed some assurance that you truly considered this a team effort. And now I have it.
Thunderwing: Then where can we find this prince? Where is his castle?
Pythor P. Chumsworth: Castle? [laughs] No, Prince Optimus lives above a library in Ponyville. Castle? [laughs]
Thunderwing: Not for much longer.
[Thunderwing destroys the stained glass window with Optimus's picture on it and goes off to find Optimus]