They were teasing Sabrina, but Netflix snatched the show from them. It's likely one of the reasons the season became disjointed, they had to scramble.
And sadly it's for the worst, because that was easily the best episode all season.
That's not really how rights work. A crossover isn't out of the question, but they can't freely use whoever they want on any network.
Crossovers across networks are usually not forbidden, they are just harder to organize. At least it is filming in the same area.
Probably not the best joke to make about traditional Samoan tattoos
Why would Reggie get his own stories? He's like a tertiary supporting character and not even friends with any main character. Kevin got Moose, I think they're going to do something with them dating.
Because Reggie is easily the 5th most important Archie Comics character (and a pretty great one at that)?
It doesn't really matter if he's important in the comics, so far he hasn't been important in the show and I don't see the appeal, in season one he was the douche who did douchey things, in season 2 they added drug dealing ... yay? Maybe I just forgot (which is possible because the middle of season 2 bored me) but does he have any redeeming qualities? Even Penelope Blossom of all people got a nice moment when she burned the St. Claire check.
Season 1 Reggie had my favorite interaction in the show.
Of course it matters that he's an important character in the comics. He's one of the best and the show hasn't done anything with him. That's the problem.
