Warning: The following contains SPOILERS for The Sandman season 1.
The third episode of Netflix's The Sandman season 1, "Dream a Little Dream of Me," is full of references to John Constantine and his comic book, Hellblazer. This is unsurprising, given that the episode is a faithful adaptation of The Sandman #3, which was also titled "Dream a Little Dream of Me," and teamed the infamous working-class warlock with Lord Morpheus, Dream of the Endless. What is surprising, however, is how many Easter eggs the Netflix series contains regarding Constantine's solo adventures that were not in the original Sandman story.
Created by Alan Moore, Stephen R. Bissette, Rick Veitch, and John Totleben, John Constantine was originally a supporting character in Swamp Thing. The con-man conjurer proved popular and was soon appearing in other comics before earning his own mature readers solo series. While some prefer the more realistic stories published by DC's Vertigo imprint, the past decade has also seen Constantine making more appearances fighting alongside the World's Finest superheroes as part of Justice League Dark.
Netflix's The Sandman does not include John Constantine due to the decision to double-cast Jenna Coleman as two versions of Johanna Constantine. One is a female version of John Constantine who exists in modern London, while the other is an ancestor, Lady Johanna Constantine, who was alive during the French Revolution. Despite this change-up, which helped the series avoid potential complications regarding the character rights to John Constantine, Netflix's The Sandman still gives a number of nods to John Constantine's life in the pages of Hellblazer.
The Newcastle Incident
The nightmare sequence that opens "Dream a Little Dream of Me" is a largely faithful reproduction of the Newcastle Incident. First depicted in Hellblazer #11, this was the case which set a young John Constantine on the road to Hell after he botched an exorcism while trying to banish the demon summoned by an even more inexperienced magician. The only major change in this sequence is that John Constantine had a crew, whereas Johanna Constantine works alone.
The Casanova Club
The opening shot of Johanna Constantine's nightmare shows her pulling up outside an establishment called the Casanova Club. This was the name of the club where the Newcastle Incident took place in the comics. The club's owner, Alex Logue, also makes an appearance in the episode.
Mucous Membrane
Before becoming a supernatural detective, John Constantine was part of a punk band called Mucous Membrane. The band is given a shout-out in one of the posters in the Casanova Club, but with the name spelled "Muchas Membrane." This may be meant to evoke other bands with intentionally misspelled names, like Megadeth or Def Leppard.
Astra Logue
John Constantine spent several years after the Newcastle Incident in an asylum, tormented by recurring nightmares of a girl named Astra Logue being dragged through a portal into Hell and being left clutching her severed arm. Johanna Constantine experiences the same nightmare in Netflix's The Sandman, and Morpheus confirms that her nightmare is no fiction of his but a true memory of Johanna's past. Thankfully, John was eventually able to rescue Astra from Hell in the pages of Hellblazer.
Rick The Vic
Rick the Vic was an Anglican vicar, who was first seen in Hellblazer #60 as part of the group of friends assembled for John's 40th birthday party. Sharing John's affinity for blasphemy and magic, Rick once officiated a combination Black Mass/Sunday Church Service in order to win a bet with the Pope. Netflix's The Sandman introduces their own version of Rick the Vic, who is a woman and apparently an occasional lover of Johanna Constantine.
Royal Blood
It is revealed that Ric the Vic summoned Johanna Constantine in Netflix's The Sandman to secure her help in banishing a demon she believes has taken possession of a British princess. This seems to be a nod towards Royal Blood, a four-part storyline which pit John Constantine against a demonically possessed British Prince (unnamed for legal reasons) who was taken over by the same demon responsible for the Jack the Ripper killings over a century earlier.
Agilieth
Morpheus helps Johanna Constantine out by identifying the demon in question as Agilieth. This is also the name of a minor demon who appeared in Hellblazer #196. Agilieth claimed to be the brother of Negral, who once gave John Constantine a demonic blood transfusion. He was ripped apart by Negral's daughter, Rosacarnis, for defying her orders to leave Constantine alone as part of her own schemes for the warlock.
Chas and Renee Chandler
While John Constantine is not in Netflix's The Sandman, his best friend and chauffeur does get a shout-out in the series. Cab driver Chas Chandler and his wife Renee are mentioned when Johanna confronts her ex-girlfriend Rachel, and Rachel lists a number of Johanna's friends she tried calling to learn why Johanna seemed to be ghosting her. This is rather amusing, as the Renee Chandler in the comics does not approve of John Constantine at all and would likely punch anyone who suggested he was a friend of hers. Presumably things are different between Renee and Johanna in the world of Netflix's The Sandman.
Oliver, Sarah, and Kit Ryan
Rachel goes on to list several of Johanna's former lovers whom she tried calling in the hope that they might have some idea of how to get a hold of her. Presuming that Johanna Constantine and John Constantine have similar tastes in lovers, the list of names references several of John's exes in the comics. Sarah was a woman John dated briefly at the start of the "Rake at the Gates of Hell" storyline. Mention is also made of a man named Oliver, which was the name of John's boyfriend in the Constantine: The Hellblazer series.
Rachel also mentions someone named Kit Ryan, which is a name of special significance to John Constantine fans. Kit was John's girlfriend throughout much of Garth Ennis' run on Hellblazer and is widely considered to be the great lost love of his life. This is particularly notable, as John did not start dating Kit Ryan until after the events of The Sandman, suggesting that Johanna Constantine's background is radically different from that of John Constantine and that she may have ruined her own love life even faster than he did.
The Sandman season 1 is now streaming on Netflix.