The CW has released its first official poster for the December Arrowverse crossover, titled Elseworlds, and I have no idea what is going on.

The poster features Arrow star Stephen Amell and The Flash star Grant Gustin in costume. The tagline reads “Destiny will be rewritten.” So far it all sounds pretty typical.

There’s just one catch.

They are in each other’s costume.

“My name is Barry Allen and I am the fastest man alive,” Amell tweeted, before adding,

So, what the heck is going on? Let’s examine what we know about the crossover so far.

Elseworlds

Elseworlds is a comic imprint that publishes non-canon DC Comics stories. The first Elseworlds story was 1989’s Gotham by Gaslight, which featured a Victorian Era Batman tracking Jack the Ripper in Gotham City. Other Elseworlds stories include 1991’s Batman: Holy Terror and 2003’s Superman: Red Son (which, notably, serves as the inspiration for the current season of Supergirl).

Though these stories were originally designed as separate from the DC canon, some have been incorporated into the DC canon using the concept of the Multiverse.

Returning characters

Characters from three of the four Arrowverse show will appear in the Elseworlds crossover: Arrow, The Flash and Supergirl.

Alongside the main characters from these three shows, we also know that Tyler Hoechlin’s Superman will appear. In fact, Amell tweeted a picture of himself, Gustin and Hoechlin on set of the crossover:

Hoechlin’s black Superman suit stands out in this shot; as with the characters from Earth-X last season, might this be an alternate version of Clark?

Casting

The most notable casting for the crossover was that of Ruby Rose as Kate Kane, aka Batwoman. We have also gotten a first look at her in the Bat cape and cowl:

Another big casting announcement for the crossover was that of Grimm star Elizabeth “Bitsie” Tulloch as Lois Lane. “This dogged, determined and brave reporter will make for a strong partner to Superman,” Supergirl EPs Jessica Queller and Robert Rovner said.

In a fun bit of casting, Stephen Amell’s real-life wife, Cassandra Jean Amell, was cast as Nora Fries, the wife of Mr. Freeze. The classic DC baddie will not be appearing in the crossover, however.

Lost alum Jeremy Davies will play John Deegan, a doctor at the Arkham Asylum for the Criminally Insane, in the crossover. According to The CW, Dr. Deegan’s “machinations will draw Green Arrow, The Flash and Supergirl to Gotham City.”

And in what seems to be a nod toward Crisis on Infinite Earths (which is being more than hinted at in the new season of The Flash), LaMonica Garrett will appear in the crossover in the “prominent role” of Mar Novu aka The Monitor, “an extraterrestrial being of infinite power.”

In the comics, The Monitor is an omniscient observer of the Multiverse who steps in to recruit heroes from the various universes in Crisis on Infinite Earths when his dark opposite, Anti-Monitor, attempts to destroy the Multiverse. There are currently 52 Monitors in the DC comics, one for each universe. (Noteworthy: Barry Allen sacrifices himself to stop Anti-Monitor and stays dead for 23 years.)

Other teases

Stars of the Arrowverse have been teasing the filming of the crossover. Aside from the posts above, Amell tweeted a photo of himself and Gustin in matching biker outfits:

He also tweeted about filming for Supergirl:

Arrow‘s David Ramsey also jumped into teaser mode:

Whatever happens, it sounds like this year’s crossover will be a wild ride!

The Arrowverse crossover will begin Sunday, December 9 with The Flash, followed by Arrow on Monday, December 10, and Supergirl on Tuesday, December 10. Each episode will air at 8:00 p.m. ET on The CW.