She could get injured. The tentacles are strong, and if they squeeze too hard, Black Cat might end up with broken bones or bruises.
One possible plot could be that Black Cat is on a heist in a place where Dr. Octavius also has an interest. His tentacles might squeeze her as a way to stop her from getting to a valuable item first. This could lead to a power struggle between them where Black Cat uses her agility and thieving skills to try and escape the grip of the tentacles.
One possible scenario is when the Black Cat and the male character MJ is interested in, say Spider - Man, have a secret mission together. MJ might find out about it and feel left out, leading to jealousy. Another scenario could be if the Black Cat flirts openly with the character and he seems to enjoy it. MJ would then feel jealous as she might think she's losing his attention.
In their personal lives, it would be chaos. Spider - Man has his relationships with Aunt May, Mary Jane, etc. Black Cat would have to navigate those while in his body. And Spider - Man would have to handle Black Cat's relationships with her criminal contacts. Their identities would be at risk of being exposed as they struggle to act like the other in their respective personal and superhero lives.
One possible plotline could be the Black Cat character forming a relationship with another female character in the Marvel universe. They might start as allies in some sort of adventure and gradually develop romantic feelings as they face challenges together and discover more about each other.
One reason could be to create a shock factor. It goes against the typical hero - villain dynamic we expect. Another might be to explore a darker side of Black Cat's character, showing her capable of extreme actions.
One possible plotline could be that the black cat has a closer relationship with MJ's love interest. So MJ feels jealous as she sees the black cat getting more attention from the person she likes.
He could lose his friends. In the original story, his friends stand for good and oppose black magic. If Harry starts learning it, they might turn their backs on him. Also, he could be ostracized by the wizarding community. The wizarding world has a clear stance against black magic, and Harry would become an outcast.
It could also cause a stir among the portraits in Grimmauld Place. The other portraits might side with Mrs Black and start to give Harry a hard time whenever he is in the house. Or, some portraits might be secretly impressed by Harry's courage and start to question their own long - held beliefs.
One possible consequence could be his expulsion from Hogwarts. Using black magic is strictly prohibited in the wizarding world, and the school has a zero - tolerance policy. Another consequence might be the loss of his friends. His friends, who uphold the values of good magic, might not be able to accept his use of black magic.
Well, if Sirius Black hates Harry Potter fanfiction, it could lead to a divide among fans. Some fans might respect his view and be more critical of fanfiction themselves, while others might disregard his feelings. Also, it could potentially limit the creativity within the fan community as people might be afraid to create content that could be seen as disrespectful to Sirius Black's character.