The trailer for Arrowverse Elseworlds has some big reveals about the upcoming crossover event. With the mid-season finales of the three shows teaming up having aired, The CW has released one final trailer that is packed full of revelations. Some of them are simple character reveals, such as our first look at Kate Kane without the Batwoman costume. Others involve supervillains who had not previously been advertised as part of the event.

However, there was a lot of new information in the latest Elseworlds trailer. It reveals some substantial new information about the Arrowverse crossover story and hints at the ultimate identity of the mysterious Dr. John Deegan at the center of the plot, and the strange book he is given that has the power to rewrite reality.

Related: Arrowverse Elseworlds Tease Explained: 1990s Flash vs The Monitor

With three different shows colliding, a new superhero being introduced, and some very weird body-swapping going on, let's see what we can figure out from the new Arrowverse Elseworlds trailer.

12. Oliver Queen & Barry Allen React To Swapping Bodies

Elseworlds Oliver Queen and Barry Allen

One of the first big reveals regarding Elseworlds was that Oliver Queen and Barry Allen would be trading places for the duration of the event. The opening scenes of the trailer show that the two heroes have swapped bodies, a la Freaky Friday, rather than reality being rewritten so that Barry Allen was stranded on Lian Yu and Oliver Queen was struck by lightning. This point is further emphasized as Caitlin Snow asks a confused Oliver Queen if he's sure he didn't go back in time and accidentally change the timeline again. Barry Allen, in Oliver Queen's body, insists that he is Barry Allen.

11. Elseworlds' Villain Gets The Book of Souls

Elseworlds The Book Of Destiny

A new scene shows Dr. John Deegan being handed a large book by an alien being and being told to "reshape the world as you see fit." Both the book and the alien being (previously identified as a Monitor) appeared in the Elseworlds prologue. The book has not been identified by any particular name yet, but it resembles The Book of Souls - an artifact in the DC Comics Universe that is capable of rewriting reality and is usually possessed by Destiny of The Endless, from Neil Gaiman's Sandman.

10. 1990s Flash Enters The Arrowverse Crossover

Elseworlds John Wesley Shipp The Flash Earth-90

Another early revelation regarding Elseworlds was that it would feature the version of Barry Allen played by John Wesley Shipp on the 1990s The Flash television series. Now identified as The Flash of Earth-90, this Flash appears in a new scene in the new trailer, warning us that "... a Crisis is coming." The classic DC Comics had several major events which were labeled with the word "Crisis" but the most famous of these - Crisis on Infinite Earths - has been hinted as a probable future event for the Arrowverse since the first episode of the 2014 Flash series.

9. Kate Kane Rains On Your Parade

Elseworlds Ruby Rose as Kate Kane Batwoman

The trailer gives us another look at Batwoman in action, apparently fighting Cisco Ramon. When Cisco asks who she is, the action suddenly cuts to a clip of a Ruby Rose, not in the Batwoman costume, saying "The rain on your parade." This is the first time that we have seen the actress in something relating to the crossover event where she wasn't dressed up as Batwoman.

Related: Arrowverse May Be Teasing The Joker In Elseworlds Crossover

8. Team Flash Turns On Barry Allen

Elseworlds Harltey Sawyer as Ralph Dibny Elongated Man

There is a rather lengthy sequence in the trailer where Oliver Queen yells at Barry Allen that he was betrayed by his team and that they weren't there for him when he needed them. This begins with a scene of Barry Allen being knocked out by a clearly distraught Elongated Man. There's no indication of why Team Flash might turn on Barry, but a safe bet is they may be afraid he's lost his mind if he continues to insist that the real Barry Allen is Oliver Queen and vice versa.

7. Killer Frost Working With ARGUS?

Elseworlds John Diggle and Killer Frost

During the sequence in which Oliver Queen shouts at Barry about being betrayed by Team Flash, we get another quick clip that seems to show Killer Frost and John Diggle together.  Killer Frost has her hair done in an intricate braided style and also seems to be wearing a black ARGUS uniform. This presents an interesting possibility: could Caitlin Snow's disassociated personality have a separate physical presence in the world of Elseworlds, who is employed by ARGUS? Or is Killer Frost just temporarily working with ARGUS?

Page 2: Black Suit Superman, Reverse Flash Returns, & More!

6. The Scientists At Work

Elseworlds Curtis Holt Caitlin Snow Felicity Smoak John Diggle

John Diggle and Caitlin Snow figure into another scene later in the Arrowverse Elseworlds trailer. The quick clip shows them, along with Curtis Holt and Felicity Smoak on a rooftop, in the middle of a storm that is sparking red lightning, while crowding around some kind of device. There is no indication what the device is or what the storm means but it is nice to know that Team Flash and Team Arrow's tech-support will have a role to play in Elseworlds as well.

5. An Angry Superman In A Black Suit

Elseworlds Tyler Hoechlin as Superman Black Suit

As The Flash of Earth-90 declares that what happened to his Earth will not happen to this one, we see a quick clip of Tyler Hoechlin in a black Superman costume.  While it has been known for some time that Hoechlin would be appearing in the darker costume, we still don't know precisely why. The clip shows that this Superman is clearly not happy, however, and he seems to be standing inside the STAR Labs building of Earth 1. There have been several theories as to the identity of this black-suited Superman, but the most horrifying possibility is that he is the Arrowverse version of Superboy Prime - a Clark Kent from the comics who went utterly mad after losing his Earth during a reality-altering battle.

Related: What Elseworlds Means For The Arrowverse & Batwoman

4. The Reverse Flash Returns

Elseworlds Tom Cavanagh as Eobard Thawne Reverse Flash

Perhaps the biggest surprise of the trailer was the brief scene showing that The Reverse Flash will be a part of Elseworlds as well. A quick clip reveals Tom Cavanagh wearing the Reverse Flash costume, taking a swing at Stephen Amell in The Flash costume. The inclusion of Eobard Thawne is particularly interesting given the revelations at the end of The Flash's mid-season finale.

3. Deathstroke Returns?

Elseworlds Deathstroke

One quick shot reveals a man fighting a group of soldiers, with a sword in one hand and a gun in the other.  Though the man lacks a certain distinctive eye-patch and the actor doesn't look like Manu Bennett, the orange and blue armor he's wearing suggest that he's an alternate-Earth version of Deathstroke or one of Slade Wilson's sons, following in his footsteps. One big question to consider: if this man is Deathstroke, which side he will be fighting on?

2. A Frightened Killer Frost

Elseworlds Danielle Panabaker as Horrified Killer Frost

Killer Frost is known for being cool under pressure (pun very much intended.) Whenever the composure of the infamous ice queen is broken, you know things are bad. While we know big things are bound to happen as a result of Elseworlds, this quick reaction shot of a clearly terrified Killer Frost speaks volumes as to just how world-shaking this event will be.

1. Doctor Destiny Revealed

Elseworlds Amazo

The penultimate scene of the trailer reveals a figure clad in strange armor that lights up with a golden glow, as The Monitor says "Show them what a real god can do." The mask of the armored suit has a distinctive skull design that is quite disturbing and horrifying. This would seem to confirm earlier speculations that Dr. John Deegan is meant to be the Arrowverse version of the classic Justice League villain Doctor Destiny, who wore a skull mask, possessed similar powers to alter reality and whose real name was Dr. John Dee.

More: Every Reveal From The Arrowverse Elseworlds Crossover Set Photos