If you guys watch Thomas Sanders, I have a long list of theories for you;
Can we just talk about when Deceit showed himself, he wasn't looking at the camera or Thomas? He was eying the spot where Virgil was standing. And Virgil was glaring back. By my theory, Virgil was supposed to be a "Dark Side" to Thomas and Deceit was also a Dark Side so it made Virgil feel that Deceit is his only friend. After a while, he figured out he was being used by Deceit. That's why he wanted to be their friend from the beginning. And also, Logan keeps screaming FALSEHOOD right? Makes me believe that he actually senses Deceit's presence but he made Logan not tell his name so he used a synonym. And can we just talk about how nice he's been to Roman, out of all the people? He's planning to make Roman fall like Virgil once did so he could make Thomas get more creative with his lying. As for Patton, since he is the most reasonable out of all the sides, it would be the best idea for Deceit to impersonate him than the other three Sides. As we see in previous videos of the Sander Sides, Thomas has a strong trust with Patton and therefore, makes it easier for Deceit to manipulate Thomas into lying to Joan (which he thankfully didn't do)
Conclusion of the story? DECEIT IS A JERK FACE (or snake face in this case)