My headconnon is that Trevor has a sister, who also so happens to be one of the Marra.

She has the same hairdo as her mom and everything.

I feel like the show never really explored how the Marra seem to have regular lives outside of being nightmare spirits, and this would be. just. such a good way to do that. This Marra, I’ll call her Jen for now, could probably relate to Trevor over his disliking of Hilda, which would be interesting, but even better would be that she can’t tell him why she dislikes Hilda. I get the feeling that becoming an Ethereal Spirit of Nightmares isn’t something you would bring up over dinner.

Jen’s family, her brother included, seem to dislike and fear the supernatural, so keeping her life as a Marra a secret would be a high priority. Imagine, Trevor venting about how he can’t prove Hilda is a witch (cuz’ she’s not be he doesn’t think that) and how he’s getting more frustrated by the supernatural every day, and she just has to sit there and listen, pretending to not be incredibly worried.

I can just imagine Trevor going out on missions to spy on and “expose” Hilda (because I also think we haven’t explored his potential as a minor antagonist) and Jen has to tag along, because a) she doesn’t want her bro to get hurt, and b) she doesn’t want her bro to get anywhere close to finding out anything about the Marra.

But Hilda gets into a lot of danger, and someday, that danger could come to Trevor on the sidelines, and she might have to expose herself to keep him safe.