Hi! Nope, it can be from different fandoms. Like I did Buck from 9-1-1 and originally had Doctor Strange from Marvel, but then I watched the premiere episode and changed it to another character from 9-1-1 Eddie. So it's totally up to you. That is totally fine. And as a Horror fan, I so approve! I LOVE Halloween/Michael and Buffy. I'm gonna be excited to see that set if you do so.