The twin could change a lot. He might be the one who stops Draco from making some really bad decisions. For instance, if Draco was about to follow Voldemort's orders blindly, the twin could convince him otherwise. This would then change the whole course of Draco's actions and how he interacts with Harry Potter and his friends.
The twin could be a new rival for Harry Potter. Instead of just Draco, now there are two Malfoys to deal with. This would make things more difficult for Harry and his friends. Maybe the twin is even more cunning than Draco and comes up with new schemes to undermine Harry at Hogwarts.
Well, they could have a very complex relationship. On one hand, they might be extremely competitive, always trying to outdo each other in everything from academics to impressing their parents. Since they are in Slytherin, they could also team up and be a formidable duo, using their combined wits to get what they want in the wizarding world. Maybe they have a secret pact to protect each other no matter what.
He could be resentful at first. After all, his parents have kept this big secret from him his whole life. But as he gets to know his twin, he might develop a sense of brotherly love. He may also start to question his family's values and actions in hiding his brother, which could lead to a change in his own character.
Self - discovery is also very common. Growing up as a Malfoy in the shadow of her brother, the sister often has to figure out who she really is. Is she just a Malfoy by name or does she have her own unique magic and personality? Fanfictions explore this by showing her journey, like learning new spells on her own or having a different view on the wizarding war than her family.
One plot idea could be that Draco's twin sister is secretly a supporter of the Order of the Phoenix. She could be working undercover within the Slytherin house to pass information to the good side. Another idea is that she has a special magical ability that Draco doesn't, like the power to communicate with magical creatures in a unique way. This could lead to adventures where she uses this ability to solve problems or help her friends. Also, she might have a love story with a Gryffindor, which would cause a lot of tension between her and her family.
Maybe the twin brother has a special power that Draco doesn't. For example, he could be a seer like Trelawney but more accurate. His visions could show him the future of Hogwarts and the wizarding world during the dark times of Voldemort's return. He then tries to use this power to prevent bad things from happening, but Draco is suspicious of his actions and tries to stop him, thinking he's going against their family and the Dark Lord.
One popular Draco Malfoy twin sister fanfiction is 'The Malfoy Heir'. It delves into the unique relationship between Draco and his sister in the wizarding world. The story often shows how she navigates Hogwarts life, dealing with the Slytherin house politics and her own identity within the Malfoy family.
The dark twin can act as a source of conflict. It might drive Harry to make different choices, leading to a completely different plot direction. For example, if the dark twin is more power - hungry, Harry might be influenced to seek out darker forms of magic.
It could lead to all sorts of interesting plot twists. Maybe there's competition or a stronger bond between them.
It would likely make Draco more self - reflective. Discovering a twin would force him to question his own identity. He might start to see himself not just as a Malfoy heir but as an individual separate from the expectations placed on him by his family.
At first, it could be strained. Draco, being used to being the only son in the family's eyes, might feel threatened by his twin. He could be jealous if his twin shows more magical talent or is more popular at Hogwarts. But as they grow older, they might start to understand each other better. For example, if they face a common enemy, like a bully from another house, they could come together and realize the importance of family.