I'm not sure who 'Perdona' is. If 'Perdona' is a person, without more context, it's difficult to say whether they have seen a ghost story. Maybe if they like spooky things or are into horror literature or movies, they might have.
I don't have enough information about this House Castillo from the novel. However, it might be a powerful and influential house. It could have a large estate, many servants, and be involved in politics or trade. Maybe it has a unique culture within it, like special feasts or ceremonies.
In terms of the plot, it could start with Sombra's return or some sort of threat that he poses. Luna then steps in to deal with it. The setting within the My Little Pony world would be important. It could be set in Canterlot or some other location. The fanfic might also introduce new characters or use existing ones to support the main plotline between Luna and Sombra.
Obviously, the princess would be one of the main characters. There might also be a charming prince or a dashing knight as the male lead. And there could be a scheming villain, perhaps an envious noble or a power - hungry courtier.
One interesting aspect could be its setting. It might be set in a grand, fictional kingdom which adds a touch of magic and allure. The characters in 'la princesa' are likely to be complex and well - developed, with the princess herself having a unique personality.