An OC can be well - integrated by having a backstory that ties into the existing lore. For example, if the OC has a family connection to an existing wizarding family or a significant event in the wizarding world's history. Also, their magical abilities should be in line with what we know about magic in the Harry Potter universe. They can't have some completely out - of - the - blue superpower.
Give the OC a unique skill or trait that is relevant to the Sherlock universe. It could be something like an eidetic memory or a talent for deciphering ancient codes. This way, they can interact with Sherlock and the other characters in a meaningful way, either as an ally or an adversary.
To integrate an OC well, first, consider their personality. If the OC is a confident and brash character, they could contrast with Android 21's more complex and often reserved nature. Second, think about their goals. If the OC's goal is to find a cure for a certain disease that Android 21 might be related to in some way, it creates an instant connection and a plot thread. Third, make sure their appearance also fits the DBZ aesthetic, like having a unique fighting gi or a distinct hairstyle.
The OC can be strong by having unwavering moral principles. For example, if Draco tries to bully someone, the OC stands up to him firmly, not afraid of his family name or his Slytherin cronies. Also, the OC can be highly intelligent in a different way than Draco. Maybe she's excellent at non - verbal magic or has a deep knowledge of ancient runes that Draco respects and is a bit envious of. This makes her a force to be reckoned with in their interactions.
One possible fanfiction idea could be that Draco Malfoy is secretly bitten by a werewolf. He then has to struggle with this new identity while still trying to maintain his status in the Slytherin house. He might be in constant fear of being discovered, especially by his pure - blood family who have high expectations and strict views on blood purity.
The OC can be integrated by having a unique talent related to a cappella. For example, if the OC has an extraordinary beatboxing skill, it can be a great addition to the group's performances in the fanfiction. This would make the OC valuable to the Pitch Perfect crew and give them a reason to be part of the story.
The Wendigo could be a creature that exists in a hidden part of the wizarding world, perhaps deep in the mountains near Hogwarts. Wizards who go astray might encounter it. For example, a group of students on an unauthorized adventure could stumble upon the Wendigo's lair.
One way is to make Krampus a guardian of some sort of ancient magic that is hidden in Hogwarts. The magic has been dormant for years, but with Voldemort's rise and fall, certain dark and light magic has been shifting. Krampus emerges to protect this magic from being misused. Harry and his friends initially see him as a threat but later realize his true purpose and help him in his mission.
The oc should have a backstory that ties in with the supernatural world. If it's a world of demons and angels, the oc's past could involve some sort of encounter with these beings that led them to be in this world now. This makes their presence more believable.
A Zoro OC can be well - integrated by having a connection to the existing world of One Piece. Let's say the OC has a dream related to the All Blue, just like Sanji. This connection to an existing concept in the One Piece universe makes the OC feel more at home. Their relationships with other characters are also crucial. If the OC has a friendly rivalry with Zoro, similar to Zoro's relationship with Sanji, it adds depth to the story. They can compete in sword - related challenges and in the process, both grow as characters.
The OC's personality should complement or contrast with Deadpool and Cable's. If the OC is very morally upright, it can create great tension and comedic moments when paired with Deadpool's morally ambiguous nature and Cable's more rigid code. Also, giving the OC unique abilities that are relevant to the story's plot, like an ability to heal that is crucial in a battle - ridden fanfic world of Deadpool and Cable.