Holly was definitely wearing a Tyler Perry productions quality wig.
Her hair was looking crazy throughout the whole show, sitting an extra 5 feet above her head with those faux locs- terrible. Very distracting every seen she was in bc it looked heavy on her head as hell.
I don't think that scratch was there until after the showdown with El Cuco in the cave.But anyway, didn't she come in contact with Jack a few times when they were fighting, that's what I was thinking - it just took time to manifest. And remember when the child who was at the fair with his grandfather, who stopped the "fake Claude" from grabbing him up- he had a scratch on his arm too. So I think those will be lead-ins for Season 2.
Also Jack can't transfer the control El Cuco has over him to other people.
El Cuco has to physically infect you with his mark at the base of your neck in order to turn you into his Renfield according to all evidence we were shown. And El Cuco scratches you to take your form.
If the scratch is supposed to be indicative of El Cuco not dying and now having Holly's form, I would think it is a reach, but it would be a workable angle for the show to take.
If they are trying to say Holly is the new El Cuco then I call bullshyt because they just inserted something brand new into the lore of the show in a post-credits scene without ever hinting at it's possibilities before.
And none of that explains what the hell was going on with her hair!