Welcome back to The Hollywood Reporter's weekly DC TV Watch, a rundown of all things DC Comics on the small screen. Every Saturday, we round up the major twists, epic fights, new mysteries and anything else that goes down on The CW's Arrow, The Flash, Legends of Tomorrow, Supergirl and Black Lightning, and Fox's Gotham. There have been a lot of news, castings and announcements all summer long about the upcoming Arrow-verse crossover event, so here is the latest piece of crucial information and what it means for the heroes …

The why of it all | Ever since it was announced earlier this summer that this year's annual CW crossover event would introduce Kate Kane aka Batwoman (Ruby Rose), speculation ran wild as to how the Green Arrow (Stephen Amell), The Flash (Grant Gustin) and Supergirl (Melissa Benoist) would end up meeting the Gotham City hero. With the latest bit of casting news announced earlier this week, some light has finally been shed on the catalyst for this year's Arrow-verse crossover. Lost alum Jeremy Davies has been cast as Dr. John Deegan in the crossover, who interestingly enough has no DC Comics counterpart. Davies will have free reign in creating an all-new villain for the huge crossover event. According to a press release, Dr. John Deegan "is a doctor at Arkham Asylum for the Criminally Insane in Gotham City, but he might just be crazier than the inmates he treats. His machinations will draw Green Arrow, The Flash and Supergirl to Gotham City." So that's how all the heroes end up in Gotham City, aka Batwoman's domain, as Deegan's actions will be so far-reaching that one or maybe even three superheroes will have to travel to a different universe.

Location, location, location | It's still unclear where exactly Gotham City is. This latest announcement still doesn't explain which universe the Arrow-verse heroes will travel to. In the past, Oliver Queen has name-dropped Bruce Wayne and Gotham on Arrow, but he was referring only to Earth-1's versions. With Supergirl's involvement in this crossover, there will be some universe-hopping already to get her in the same room as Oliver and Barry. But is she the only one traveling to a new universe, or will Kate Kane's version of Gotham City be in a new universe, meaning that Oliver and Barry need to breach to a new universe along with Kara? If the potential Batwoman series is greenlit after the crossover, having it set in the same universe as Arrow and The Flash means more opportunities for smaller crossovers in the future. If it is set in a different universe like Supergirl, the reasoning for crossovers in the future need to be bigger, meaning fewer opportunities for quick one-offs.

Some more new faces | The crossover's villain is not the only new character who will be appearing in the Arrow-verse for the first time during the three-episode run. Along with Tyler Hoechlin reprising his role as Superman, Elizabeth "Bitsie" Tulloch (Grimm) has landed the highly coveted role of "dogged, determined and brave reporter" Lois Lane for all three episodes. And Amell's real-life wife, actress Cassandra Jean Amell, will appear in the crossover as Nora Fries, the wife of iconic DC Comics character Mr. Freeze (who has not yet been featured in the Arrow-verse and will not appear in the crossover). But who even needs Mr. Freeze when Nora has the opportunity to spread her wings as the DC Comics villain Lazara all on her own? In one iteration in the comics, Nora is tossed into a Lazarus Pit by her husband after she was frozen by him to escape a terminal illness. But because she spent so long in a coma before that, Nora rose from the pit with the ability to conjure flame and reanimate the dead. She became the supervillain Lazara, and blamed her husband for her cursed state until he froze her once more. There's no word yet on which version of Nora Fries will show up in the crossover, but here's hoping that it's a female villain.

Mark your calendars now | This year's annual CW crossover is taking place over three consecutive nights. Airing in early December, the three-episode event begins with an episode of The Flash on Sunday, Dec. 9, at 8 p.m., continuing with Arrow on Monday, Dec. 10, at 8 p.m. and concluding with Supergirl on Tuesday, Dec. 11, at 8 p.m., with The Flash and Supergirl swapping nights for one time only. And bookmark this page as we update it with everything there is to know about the Batwoman crossover.