Warning: The following contains SPOILERS for The Sandman season 1.
A nightmare sequence in The Sandman episode 3 centers around the magician Johanna Constantine and a girl named Astra. The details of the bad dream are not explained beyond it being a recurring nightmare of something from Johanna's past. Fans of the comic book character John Constantine, however, are well aware of who Astra is and the significance of Johanna Constantine's nightmare.
The character of Johanna Constantine in The Sandmanhas been a source of some confusion in Netflix's adaptation. When the first wave of casting announcements listed Jenna Coleman as a character named Johanna Constantine, it was presumed she would be playing the role of Lady Johanna Constantine, who in the comics was an ancestor of the warlock John Constantine from the time of the French Revolution. It was later revealed, however, that in Netflix's The Sandman series, Coleman plays both the Lady Constantine and a new character based on John Constantine named Johanna Constantine.
Related: Why John Constantine Isn't In The Sandman
While this change might seem arbitrary, it was necessary due to the live-action character rights for John Constantine being tied up in J.J. Abrams' reboot of the Constantine TV series. However, fans of the Hellblazer comic series can take comfort in the fact that The Sandman episode 3 is packed with Easter eggs paying homage to the source material, even as it establishes Johanna Constantine as the John Constantine of this universe through her recurrent dreams of Astra.
The nightmare that opens The Sandman episode 3 reenacts the Newcastle Incident. First depicted in Hellblazer #11, the Newcastle Incident set a young John Constantine on the road to Hell
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