One common theme is the exploration of duality. Since Dream and Nightmare are opposites, many fanfictions explore how they are two sides of the same coin. For example, how Nightmare might have some good in him despite his dark nature, and vice versa for Dream.
Another theme is redemption. Some fanfictions show Nightmare seeking redemption for his actions, and Dream being the one who might guide him on that path. It's about changing and growing past their initial natures. It can be really heart - warming to see the development in these stories.
One common theme could be fear. Since it's about nightmare dreams, fear would likely play a big role. Another theme might be self - discovery. Maybe in the nightmare dreams, Chuck Casey discovers something about himself. Also, there could be a theme of survival, as he might be facing some sort of threat in these dreams.
One common theme is the exploration of the dark side. Since they are nightmare - based characters, a lot of fictions focus on their sinister nature.
One common theme is loyalty. They often show how nightmare freddy and nightmare bonnie are loyal to each other in the spooky nightmare world. Another theme is survival. Since it's a nightmare setting, they have to work together to survive against various threats.
Isolation is also a theme. In many 'tails nightmare fanfiction', Tails is often alone in his nightmares. This isolation amplifies the sense of horror and makes the reader feel more empathetic towards him. It also allows for deeper exploration of his character as he has to rely solely on himself to get out of the nightmare situation.
One common theme is the struggle between good and evil, as Dream Sans is often associated with positive aspects and Nightmare Sans with negative ones. Their relationship in fanfics can explore how they deal with their opposing natures.
One popular theme is the reconciliation between Nightmare and Dream. It often involves them overcoming their differences and past conflicts.
One popular theme could be redemption. Nightmare, being the more 'evil' of the two in the original concept, might find redemption through his relationship with Dream. Another theme could be forbidden love, as they are on opposite sides of the spectrum in 'dreamtale'.
One common theme is the struggle between good and evil within Twilight Sparkle. Since it involves her nightmare form, there's often a battle within her to resist the darker impulses. Another theme is the power of friendship. Her friends usually try to help her overcome the nightmare influence, showing that friendship can conquer even the darkest of forces.
One common theme is fear for each other's safety. Since they are in a dangerous wizarding world, nightmares often revolve around one of them being in peril. For example, Harry might dream of Ginny being captured by Death Eaters.
One common theme is the exploration of darkness. Since both characters have rather menacing aspects, fanfictions often delve into the darker sides of their existence and how they interact within that realm of darkness.