The following article contains discussions/depictions of suicide.
Spoilers for The Sandman season 1 and The Sandman comics
Every character in Neil Gaiman's The Sandman has their own story, whether they are human or an otherworldly being. Some characters such as Lucifer, Death, and Constantine had their own spin-off or separate comics, creating a precedent for TV spin-offs.
It is not only the leads that have interesting pasts. All of The Sandman's characters have fascinating backstories, with gaps worth filling, or futures worth exploring. According to an interview with Variety, Gaiman has even considered spin-off projects for both Death and Johanna Constantine, which makes it seem as though the option will be explored sooner rather than later.
Ethel Cripps
Ethel Cripps (Joely Richardson) has just as interesting a story as her son, John Dee. For years, she ed herself and John by working as a cat-burglar and making black market trades of the ancient and supernatural.
Ethel's exploits with her heists and dealings with the supernatural could make for a good monster of the week-style spin-off. It would be intriguing to explore her relationship with her son John Dee more, as well as how she first acquired her amulet from a demon. While Ethel wouldn't be the most likable main protagonist, there is a history of compelling shows with unlikable main characters.
Gilbert
Gilbert (portrayed by Steven Fry), the helpful and eccentric neighbor of Rose Walker, has a backstory worth exploring. Originally a location in the dreaming called Fiddlers Green, he set out to learn what it was like to be human when Morpheus was being held captive.
It could be worthwhile exploring all of Gilbert's earlier years when he was getting used to being human. There could be some effective fish-out-of-water storytelling as he gets used to living in the human world. The fact that Gilbert is implied to have spent multiple decades on Earth offers lots of storytelling possibilities. Perhaps he explored other parts of the world before coming to Florida.
Gault
Gault (Ann Ogbomo) is an unusual member of the Dreaming, a nightmare who is redeemed and becomes a dream by the end of season 1 for helping Jed by giving him an escapist fantasy.
Gault could have a highly compelling spin-off exploring her experience adjusting to being a dream instead of a nightmare. It could explore her relationship with dreamers and how she can help and empower them through the dreams she's in with them. It could also look into her shape-shifting abilities and how she uses them in this new context. As Gault is an original character for the Netflix series, there is a lot of untried ground that could be explored with her.
Cain and Abel
The two brothers Cain (Sanjeev Bhaskar) and Abel (Asim Chaudhry) stood out with their darkly comedic relationship of perpetual murderer and victim.
Cain and Abel would work well in a black comedy sitcom spin-off focusing on the strange relationship the two brothers have as well as showcasing their adorable pet gargoyle Goldie. It would feel satisfying to have Abel stand up to his brother Cain as the series went on. Also, it would be intriguing to explore more of the inside of their homes, the House of Mystery and the House of Secrets.
Hal Carter
There are many intriguing residents of the bed and breakfast where Rose Walker comes to stay, with the owner Hal Carter (John Cameron Mitchell, recognizable as Joe Exotic from Joe vs. Carole) being no exception. He's a good friend to Rose and a drag queen with dreams of performing on Broadway.
Since Hal decides to sell his bed and breakfast and give acting a try in New York at the end of season 1, it could make an intriguing spin-off to see him try to make it on Broadway. Perhaps he could come into with the supernatural since it would still take place in the world of The Sandman. Hal could also cross paths again with Barbie, who in The Sandman graphic novel A Game of You moves to New York City temporarily after she and Ken break up. A spin-off could also showcase more of Hal's musical numbers and his drag act.
Hob Gadling
Hob Gadling (Ferdinand Kingsley) is the man to whom Dream grants immortality. The pair meet every 100 years at the same pub, where Dream offers him either an extra century of life or to follow Death.
It could be fascinating to explore Hob's adventures in between the pub visits. He has lived such a long life and through so many time periods, that it would be compelling to explore how he reacts to all the changes. A spin-off could have a rotating cast of different characters, as time advances.
Unity Kincaid
Rose's great grandmother Unity Kincaid (Sandra James-Young) had dreams while under the sleep-sickness, something which could make for an intriguing spin-off.
Unity's false dream life could be fascinating if explored in more depth. Since Unity dreamed of the perfect life where she inherited her father's business, stayed with her lover (Desire), and had a baby, it could work as an WandaVision-esque show where Unity has this seemingly idyllic life with increasingly eerie hints that it's not real seeping through.
Desire
Desire (Mason Alexander Park) may be villainous in the first season of The Sandman, however, they could be a fascinating protagonist of their own series.
As the embodiment of lust and desire, it would be intriguing to see a show from Desire's perspective. They could show the positive side to their duties. Considering a kinder aspect was already hinted at with them in a loving consensual relationship with Unity in her dreams, and a caring relationship with their twin sister Despair, there is clearly more that could be expanded on with them.
Death
Death (played by Kirby Howell-Baptiste) proved herself to be a comionate kindhearted being who loves humans in the episode "The Sound of Her Wings" - proving that it would be worth either adapting her spin-off comics or giving her an original story.
A Death spin-off could be an adaptation of her comics, such as Death: The High Cost of Living. This would need some adjustments to retain Howell-Baptiste, however, as the comic involves Death becoming a teenage girl named Didi for a day. They would need to change this aspect, but they could keep her becoming human for a day and befriending a suicidal young man named Sexton. On the other hand, a Death spin-off could simply focus on her helping different people during their time of death, and her relationship with humans in general.
Johanna Constantine
Johanna Constantine I and II (Jenna Coleman) would both make for intriguing spin-offs. Johanna Constantine I has her own comics spin-off series, Hellblazer: Lady Constantine and John Constantine (the inspiration for Johanna Constantine II) had his own comic series Hellblazer – John Constantine.
A Johanna Constantine I spin-off would focus on her adventures doing jobs for Dream, as Dream mentioned to Hob in "The Sound of Her Wings." This could also allow for much more exploration of her past in poverty after the execution of her parents. A spin-off focused on Johanna Constantine II could explore her other cases as an occult detective, either directly adapting storylines from Hellblazer or creating new storylines - perhaps in a monster-of-the-week format.