The Latest "Elseworlds" Trailer Teases New Arrowverse Villains The Monitor & Dr. John Deegan — VIDEO

Jack Rowand/The CW

After weeks of speculation and hints of what the newest Arrowverse crossover will fully be about, the new "Elseworlds" trailer teased the Arrowverse's new villains and begins to answer the question: why are Barry and Oliver switching lives?

As already revealed, the plot of the three episodes — starting with Supergirl and continuing over to Arrow and The Flash — making up "Elseworlds" will be set in an alternate reality, where Barry Allen and Oliver Queen switch lives with one another. They have switched powers and abilities, names, and have also stepped into each other's lives (early teasers revealed Oliver — as Barry — is married to Iris, and Barry — as Oliver — is training with Diggle).

As for Supergirl, Kara is still (luckily) Kara, however in this new reality Alex isn't her sister. Instead Alex calls her "despicable" and has her locked up in one of the holding cells from The Flash. She also has a House of El symbol on her uniform, so she might be working for Kara's cousin Kal instead (and possibly in the reality where Kal is the Black Superman).

And finally, in the newest "Elseworlds" trailer, fans finally get to see why all these things are happening, or at least, who's to blame.

In the new trailer, released Nov. 25, Barry and Oliver establish that they're aware that "something is wrong with reality," and that they've swapped places. It then shows Oliver (Barry) confront the Arkham Asylum doctor responsible, Dr. John Deegan (played by Jeremy Davies). DC fans will recognize Arkham Asylum as a famed Gotham City site, clearly paving the way for the introduction of Batwoman to the Arrowverse.

Dr. Deegan's motives remain mysterious, but the trailer does reveal who put him up to this "Elseworlds" magic, and that's The Monitor. As played by LaMonica Garrett, The Monitor is "an extraterrestrial being of infinite power," according to Entertainment Weekly. In the comics, he watches over the Multiverse in order to keep it safe from The Anti-Monitor. However, from the looks of this trailer, his motives seem a bit less noble.

In the trailer, he hands Dr. Deegan a heavy book, something that probably aided in him altering reality. "I offer you godhood," The Monitor says. Then, over footage of the black-suited Superman, he states, "Show them what a real god can do." He might still be talking to the doctor, referencing the fact that he brought about a dark version of Kal-El.

Jack Rowand/The CW

Villains aside, the new "Elseworlds" trailer is just so full of content. It confirms that Killer Frost will appear in the crossover event, and also reveals some new Batwoman footage. Finally, the clip also features John Wesley Shipp's return as a The Flash, saying, "You will not do this earth what you did to mine," suggesting a past with The Monitor.

With all these heroes, both new and returning, and two new villains to contend with, this year's Arrowverse crossover event is already looking a bit overwhelming. But, with three full episodes to dive into all the characters and new conflicts, it also looks like "Elseworlds" is going to be very satisfying.