Here are all the details so far on the annual Supergirl, The Flash, Arrow, and Legends of Tomorrow crossover, "Invasion!"

With the fall television season in full swing, The CW is building towards their annual crossover event with their superhero shows, this time, it will feature FOUR shows, not three. And what threat could be big enough? That would be DC’s genocidal aliens The Dominators!
Anyone not familiar with obscure interstellar comic book storylines might be asking themselves, "who?" Well, try to envision the genetic-tinkering giant Engineer from Prometheus, only as spindly, yellow-skinned, pointy-eared, claw-handed, robe-wearing Star Trek-like villains, each sporting a massive red circle on the forehead, the size of which determines their individual caste.

You can totally check out The Dominators in this bit of archival "found footage" indicating that the Dominators have been messing around on Earth for much longer than we thought...
Oh, and there are some other surprises in this next trailer, including a new costume for a new member of the Legends of Tomorrow team, and the return of a big Arrow villain.
Check it out:
Here's an earlier teaser, too...
First appearing in Adventure Comics #161 in 1967, the cosmos-cavorting scientist species the Dominators would often pester the Legion of Super-Heroes, though they never quite resided in the A-list category of DC Comics rogues. However, the Dominators did eventually become the centerpiece of a 1989 comic book crossover by Keith Giffen, Bill Mantlo, Todd McFarlane, and others called Invasion! in which a group of DC’s players came together to stop their plot to use a potent global WMD called a Gene Bomb designed to wipe all metahumans from the face of the Earth.
The crossover kicks off on November 28th. We've got the first official story details for each chapter of the event right here...
Supergirl Season 2 Episode 8: Medusa
Eliza (guest star Helen Slater) comes to town to celebrate Thanksgiving with her daughters. Alex (Chyler Leigh) decides it’s time to come out to her mother; Kara (Melisa Benoist) is shocked when Eliza suggests Mon-El (Chris Wood) has feelings for her, and Winn (Jeremy Jordan) and James (Mehcad Brooks) consider telling Kara the truth about the Guardian. Meanwhile, CADMUS unleashes a virus that instantly kills any alien in the vicinity so Kara enlists an unexpected ally – Lena Luthor (Katie McGrath). The epic superhero crossover kicks off tonight when Barry Allen (guest star Grant Gustin) and Cisco Ramon (guest star Carlos Valdes) seek Kara’s help with an alien invasion on their Earth.
air date: 11/28/16
The Flash Season 3 Episode 8: Invasion!
When aliens called the Dominators attack Central City, Barry (Grant Gustin) speeds over to Star City to ask the Green Arrow (guest star Stephen Amell) for help in stopping them. Realizing the battle against the Dominators is bigger than they thought, they track down the Legends of Tomorrow, and Barry and Cisco (Carlos Valdes) create a breach to bring back a secret weapon – Supergirl (guest star Melissa Benoist). Once all of the super friends are assembled, they come up with a plan to attack but a shocking secret related to Flashpoint is revealed and suddenly no one is sure who they can trust. Meanwhile, Wally (Keiynan Lonsdale) wants to join the battle against the aliens but Iris (Candice Patton) tells him he’s not ready.
air date: 11/29/16
Arrow Season 5 Episode 8: Invasion!
Oliver (Stephen Amell) wakes up to a life where he never got on The Queen’s Gambit. Robert (guest star Jamey Sheridan) and Moira Queen (guest star Susanna Thompson) are alive and well. Laurel (guest star Katie Cassidy) is his loving fiancée and their wedding is imminent. Everything seems perfect, but Oliver starts to notice small imperfections that make him question this new reality. Meanwhile, Felicity (Emily Bett Rickards) and the recruits take on a new threat with help from The Flash (guest star Grant Gustin) and Supergirl (guest star Melissa Benoist).
air date: 11/30/16
Legends of Tomorrow Season 2 Episode 7: Invasion!
After learning the Dominators’ plan for the world, the Legends must work together with The Flash (guest star Grant Gustin), Supergirl (guest star Melissa Benoist) and Green Arrow (guest star Stephen Amell) to kill them once and for all. Meanwhile, Stein (Victor Garber) figures out, with the help of others, how the team can terminate the Dominators, but is distracted by the aberration he realizes he created in 1987. Brandon Routh, Franz Drameh, Dominic Purcell, Maisie Richardson-Sellers, Nick Zano and Caity Lotz also star.
air date: 12/1/16