"Great and...Powerful?" The mechanical harpy blinked, more for emphasis then anything else. "Be that as it may, I have no idea how you managed to get aboard my ship, two hundred feet under water I might add, cart and all, but you can't stay here." 🎀 He reached into a box and pulled out a frankly obscenely expensive looking ribbon. "Here-" Derel stuck it too Trixies collar, her chest pushing the bow up into her face, "a valuable trinket, so you can leave agreeably when we surface."
Being honest, even Trixie didn't know how she got down here. She was just practicing a simple teleportation spell with Starlight Glimmer, and next thing she knows, she finds both herself and her home within a submarine! At least, it can be assumed it was a submarine thanks to what Derel had told her. As for when she was given her little present by the submarine captain - another thing which can be assumed since he called it 'his ship' - the stage magician couldn't help but grin.
"While it is quite small, it seems like a fitting prize for the Great and Powerful Trixie!" Trixie boasted, pretty much introducing herself to Derel under the same instance. "As for waiting for us to arrive at the surface, I will not need to wait for such a task to finish. Now watch, as I use my magic to make myself vanish before your very eyes!"
Trixie then attempts to use a teleportation spell on both herself, and her own cart in order to teleport both objects back to Ponyville, but unfortunately found herself unable to do so. The cart was already very big and heavy and hard to teleport as is, but when your own figure consists up beanbag sized boobs and large beachball sized ass cheeks, that pretty much makes a hard task pretty... Well, impossible. Meaning try as hard as she wanted, but the stage magician wasn't teleporting out of that submarine; And ESPECIALLY not doing it at such a huge distance and not knowing where Ponyville was from here.