Riverdale boss reveals most-debated stories and the ones he's proudest of as series hits 100 episodes

For 99 episodes, Riverdale has delivered shocking twists, swoon-worthy ships, unforgettable musical numbers, and countless poor decisions by Archie Andrews (KJ Apa). Now, as it wraps up its five-episode event in Rivervale, it's celebrating its 100th episode with an hour about the very comic books that inspired the series.

But before we watch that, EW spoke with showrunner Roberto Aguirre-Sacasa about the series' run so far, the most-debated stories, and more.

The moment he knew it was a hit

"One big moment happened after the season 1 premiered on The CW and then it all appeared on Netflix," says Aguirre-Sacasa. "Riverdale was one of the early shows from the CW that migrated over to Netflix and that's when the show captured fan's imaginations. I remember, we hadn't yet gotten a pickup for season 2 and the show dropped on Netflix and the response was pretty robust. We didn't really understand what has since become known as the Netflix Effect, so that's a moment where it jumped from a quiet show on the CW into a slightly less quiet show. I never thought, 'We're going to make a hit show.' At best I thought, 'This could be a cult-y kind of show,' but I wasn't thinking this will be a 100-episode, multi-season show."

The episodes he's most proud of

"The pilot is, to me, still one of our most beautiful episodes. That is a really, really special episode and there was something really pure when we were making season 1, before the show even aired. Also in that first season, we made the decision to solve the mystery of Jason Blossom [Trevor Stines] in the penultimate episode and I remember that some of the executives didn't want that. They wanted the mystery to be solved in the finale and [executive producer] Greg Berlanti had said, 'Solve the mystery in the penultimate episode so that in the last episode, you can get back to all the characters and not make it about the mystery.' There was a lot of anxiety about that. At the time it was a big deal and I'm really, really proud of both the solving of the mystery in season 1 and of the finale. The finale has one of my favorite sequences, which is Cheryl [Madelaine Petsch] on the ice and Archie and the core four going to help her. There's an epic-ness to that that opened up the show."

"Another very beautiful and certainly very powerful and emotional episode is our tribute to the character of Fred and our tribute to Luke [Perry]. That was a very cathartic episode and difficult to make, but I think everyone came together and I'm so proud that we were able to honor Luke that way."

"And then on a totally different note, our musical episodes. You either love them or you hate them, and I love them! And the cast loves making them."

On which characters surprised him

"There's no predicting what will or won't connect. I do remember early on, in season 1, we wrote the episode where Betty [Lili Reinhart] and Jughead [Cole Sprouse] get together, and I remember Cole and Lili called me. They were both against them getting together so quickly. They said, 'The audience isn't going to like this, they want Archie and Betty.' I was like, 'I hear you. I think we should see.' We had a sense in the writers' room that Jughead and Betty might be a good pairing. The writers were shipping them very early on."

"I think we've done really well with adding subsequent characters that people have embraced. I'm not surprised Cheryl popped as much as she did. Madelaine came in and was incredible. When we introduced Toni [Vanessa Morgan], she was immediately embraced. When we introduced, much later in the series, Erinn [Westbrook] as Tabitha, that really worked as well."

"The other thing that worked really well was when we introduced, for instance, Skeet [Ulrich] as Jughead's father. That was a big moment for us, to get an actor like Skeet. I even remember when we were going to introduce the Southside Serpents, no one wanted the Southside Serpents. The executives would say, 'But this isn't a show about gangs.' And I remember thinking, 'Well, it's sort of like West Side Story and The Outsiders.' But when someone like Skeet came on board, it was like, 'Wow, this is great.' I often say the show wouldn't have worked as well as it did without Luke, Skeet, Madchen [Amick], Marisol [Nichols] and Mark [Consuelos]. They really legitimized the show."

On the stories that caused some debate

"I would say one of the most controversial discussions that happened early on with the executives and us was Dark Betty. When we introduced Dark Betty in episode 3, there was real concern about like, 'What's this story line? What's this show?' We even had to test the episode with an audience because people were so unsure of it. We got a call and it was like, 'Well, weirdly it tested better than the pilot and episode 2,' mostly because people were fascinated by Betty. She had gone from the girl who was pining for Archie and she suddenly became this very psychologically complex, surprising character. That was one very big debate we had around the show early on."

"We talked about, early on, how much of high school life do we want to depict. At the time, high school shows had fallen out of favor a little bit. I remember, I think it was in that third episode, there was a story line where Archie was grounded. The response was like, 'We're not really telling a story about Archie being grounded are we?' We were like, 'Yeah, that's what happens to teens.' There was stuff like that. I will say though, by and large, people supported what the show was and how strange it was. There were a lot of discussions but nothing that divided the room or anything like that. In season 1, everything's under a microscope. That's part of the journey."

Riverdale's 100th episode airs Tuesday, Dec. 14 at 9 p.m. ET on The CW.

Check out our daily must-see picks — plus news, celeb interviews, trivia, and more — on EW's What to Watchpodcast.

Related content:

• [Spoiler] is back from the dead in an exclusive script page from Riverdale's 100th episode
• Sabrina lands in Riverdale and gets right to spellcasting with Cheryl in exclusive sneak peek
• Kiernan Shipka previews Sabrina's time on Riverdale, says 'the door's open' to future stories