Supergirl
Season 3, Episode 8: Crisis on Earth-X (I)
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Barry and Iris’s wedding brings the gang together, but things go awry when villains from Earth-X attack the ceremony. All of the superheroes band together with help from their super friends like Citizen Cold, The Ray, Felicity Smoak, Iris West and Alex Danvers to take on their most formidable villains yet. Earth’s mightiest heroes – Green Arrow, Supergirl, The Flash and White Canary – lead their teams into battle to save the world. The crossover continues on Arrow S06E08 Crisis on Earth-X (II), The Flash S04E08 Crisis on Earth-X (III) and DC's Legends of Tomorrow S03E08 Crisis on Earth-X (IV).
All Episodes - Season 3
Episode 1
Girl of Steel
Episode 2
Triggers
Episode 3
Far From the Tree
Episode 4
The Faithful
Episode 5
Damage
Episode 6
Midvale
Episode 7
Wake Up
Episode 8
Crisis on Earth-X (I)
Episode 9
Reign
Episode 10
Legion of Superheroes
Episode 11
Fort Rozz
Episode 12
For Good
Episode 13
Both Sides Now
Episode 14
Schott Through the Heart
Episode 15
In Search of Lost Time
Episode 16
Of Two Minds
Episode 17
Trinity
Episode 18
Shelter from the Storm
Episode 19
The Fanatical
Episode 20
Dark Side of the Moon
Episode 21
Not Kansas
Episode 22
Make It Reign
Episode 23
Battles Lost and Won