It’s like if you took the plot of Inception, the logic of Alice in Wonderland, the setting of Bladerunner or Suckerpunch or any of the Bioshock games or Dune or whatever, and then put them all into one story.
This genre is extremely specific and there isn’t much out there in terms of literature, so I can’t really give examples of what’s been done and what tropes are necessary. At this point it’s kind of a hit or miss when entering the genre. The main requirement is that you include something relating to dreams/nightmares, but that doesn’t automatically make your story dreampunk.