Well, generally speaking, in this story, an unexpected guest shows up and disrupts the normal situation of the protagonist or the household. But without reading the specific story, it's hard to be more detailed.
Perhaps Neville's grandmother Augusta. She has always been a bit of a stern character, and at first, no one expects her to come. But she shows up with a beautiful family heirloom as a gift for Ginny. She might even give a short but heartfelt speech about how she has watched Harry grow and how proud she is of the young couple. This would be unexpected as she doesn't seem the type to be very involved in the social lives of the younger generation.
One way to get guest photos at Comic Con is to follow the event's rules and schedule. Usually, there are specific spots and times set aside for photo opportunities with guests. Also, make sure your device is charged and ready!
In most cases, Comic Con doesn't cover the flights for guests. They might offer other perks, but flight expenses are often the responsibility of the guests themselves.
The Box Ghost could be really unexpected. He's usually so focused on his boxes that seeing him at a party would be a shock. He might bring his boxes as party favors or something, which would be really odd. He could keep trying to stack his boxes in the middle of the dance floor, much to the annoyance of the other guests.
You usually need to apply through the official website and meet their specific requirements. It could involve having a significant presence in the comic industry or a related field.
My wife is very adaptable. When unexpected guests arrive, she first calms them down if they seem worried about intruding. Then she assesses what they might need, like a place to rest or something to eat. For example, one time a neighbor came over suddenly because of a problem at their place. My wife listened to her, gave her a cup of coffee, and offered some practical advice. It was amazing to see how she handled it.
An unexpected guest could be a human who has some sort of special ability to see the supernatural world but has been hiding it. This person could come forward at the wedding and reveal that they know all about the vampires and werewolves and that they have a message from a higher power about Jacob and Bella's relationship. It would be very unexpected as no one expected a normal human to be involved in such a way.