Remember Sombra? Yeah, King Sombra, the guy that once was an evil dictator and ruled over his subjects with an iron hoof. Turns out he is actually incompetent and retarded. Why? I dunno, because this is a comedy, I guess.
Being Great and Powerful is nice and all, but it takes quite a bit of hard work to get there. Luckily, Trixie knows exactly how to 'convince' people to like her and her show.
Side Story to "The Not-So-Normal Adventures of King Sombra and Pinkie Pie". It's never easy meeting your marefriend's family members. Especially when that family member is her older sister.