In season 6, episode 20, " Chapter One Hundred and Fifteen: Return to Rivervale ," the gang discovers that their current antagonist, Percival Pickens , is actually an immortal sorcerer from the parallel universe of Rivervale . Key Plot Developments
: Jughead and Tabitha travel to Rivervale, where they learn that the two universes are conjoined and bleeding into each other. They discover that a phone call from "Bunker Jughead" to Betty—warning her of the bomb—prevented a clean break between dimensions, causing the supernatural powers and Percival's arrival. [S6E20] Chapter One Hundred and Fifteen: Return...
: While Jughead uses his new portal-opening powers to rescue Reggie, Kevin, and Marty Mantle from execution, Percival retaliates by executing Alice Cooper , Frank Andrews , and Tom Keller instead. In season 6, episode 20, " Chapter One
For more details, you can read the full recap on the Riverdale Wiki or reviews from TV Fanatic and Entertainment Weekly . Chapter One Hundred and Fifteen: Return to Rivervale : While Jughead uses his new portal-opening powers