Chilling Adventures of Sabrina was initially envisioned as a direct spinoff of The CW's Riverdale. It was, in concept, going to air on The CW, probably paired with Riverdale to create an Archieland-type block of programming, with regular crossovers, not unlike Shondaland's Grey's Anatomy and Station 19. But then the show went to Netflix, and most of that got nixed, especially the crossover parts, which is why Sabrina fans were surprised to recognize Robin Goodfellow when he showed up, because the actor who plays Robin in Chilling Adventures Of Sabrina Part 3 is a familiar face to Riverdale watchers.
Warning: Spoilers for Chilling Adventures Of Sabrina Part 3 follow. Up until now, crossovers from one show to the other have been limited to easter egg references, mainly ones CAOS makes about Riverdale. Part 3 comes the closest the show has to having a real crossover when Hilda sends Dr. Cee to Pop's for takeout.
However, there's another big worlds-collide moment in the new season, and while it's not a direct reference to Riverdale, it is pretty exciting for fans of both shows. Early on in CAOS Part 3, fans were introduced to actor Jonathan Whitesell, who was just recently seen in the town next door. But he's not playing the same character in both shows, and fans who only watch CAOS will have no idea he's already a familiar face in the Archieverse.
In Riverdale, Jonathan Whitesell played Kurtz, a student at Riverdale High School. Kurtz was part of both the Southside Serpents and the Gargoyle Gang. A dangerous guy with violent tendencies, he was a fanatic member of the gang, seemed to believe the whole "Gargoyle King" was real, and became an enemy of the Jones family. The Gargoyle King turned out to be real enough to kill Kurtz anyway, cutting Whitesell's time on the show short after only a handful of Season 3 episodes.
Whitesell must have made a strong impression on the powers-that-be, because he was able to make the leap to CAOS. When Chilling Adventures of Sabrina was looking to cast a love interest for Theo in Part 3, Whitesell got the job. In this role, he plays Robin Goodfellow, a hobgoblin who is a member of the Pagan camp.
Early on in the season, the CAOS hinted Robin might be part of the tribe trying to take down the Church of the Night and sacrifice Theo to the Green Man. But it turned out Robin was good person at heart, whose feelings for Theo were real enough to turn him against his fellow Pagans. It doesn't get much more romantic in Greendale than that.
Chilling Adventures of Sabrina Part 3 is on Netflix now.