The only major connection between the new film version of Flatliners and the 1990 original is Kiefer Sutherland, who was one of the two leads of the first film along with Julia Roberts.
Presumably with more than just this one single shot of Kiefer Sutherland in it (although it would be kind of amazing if he literally appeared in one shot and no one ever discussed it or noticed him).
But as their experiments become increasingly dangerous, they are each haunted by the sins of their pasts, brought on by the paranormal consequences of trespassing to the other side.
What could possibly go wrong with that plan?
…
If the Wonder Woman TV Show Starred the Movie Cast