There's a fanfic called 'The False Identity'. The plot twist here is that the Venom symbiote that Peter bonds with is actually a fake created by a villain to manipulate him. Peter has to figure out the truth while dealing with the new powers and the false Venom's influence on his mind.
In some fanfics, like 'The Unexpected Ally', a plot twist could be that Venom actually has a hidden connection to Peter's family history. This completely changes the dynamic between them as they start to uncover secrets together.
One idea could be that Peter tries to find a way to coexist with Venom without losing his own mind. He could use Venom's powers for good in a new and unique way, like being able to heal people with Venom's symbiotic abilities. Another plot could be Venom getting separated into multiple parts and Peter has to track them all down before they cause chaos. Maybe one part of Venom attaches to a villain and gives them enhanced powers that Peter has to face.
One idea could be that the Female Venom forms an unexpected alliance with Peter Parker. Maybe she initially has her own motives but as they interact more, she starts to see the good in Peter and his mission to protect the city. They could team up to take on a new super - villain that neither could face alone.
Perhaps the plot involves Venom sensing that Peter has a pure heart despite their initial differences. Venom adopts Peter because he realizes Peter is alone in the world after some tragic event in the fanfiction. Venom then tries to teach Peter how to use his powers in a more aggressive way, which Peter is initially hesitant about but later comes to understand. This could lead to Peter becoming a more formidable Spider - Man with Venom's influence.
One plot idea could be that Agent Venom is initially sent to spy on Peter Parker, thinking he might be a threat. But as he gets to know Peter better, he realizes that they could be great allies against a common enemy, like a new super - villain in the city.
In some fanfictions, a plot twist could be Peter losing his powers and having to rely on his intelligence alone. For example, in 'Powerless Peter', he has to use his scientific knowledge to outwit villains. Another is when the alternate universe has Peter's loved ones turn against him. In 'Betrayed by Aunt May', Aunt May becomes a villain, which is a huge shock. And sometimes, Peter is from a different time period in the alternate universe, like in 'Peter from the Future', and that changes the whole dynamic of the story.
One interesting plot twist could be that Peter's spider - sense is affected by his new vampire nature. Instead of warning him of physical danger, it now warns him of approaching sunlight or the presence of vampire hunters. Another could be that his relationships with his friends and family change drastically. For example, he has to hide his new identity from Aunt May, but she starts to suspect something when he avoids going out during the day. Also, his friendship with Ned might be strained as he has to keep this huge secret.
At first, it would be really rocky. Peter would be very wary of Venom given their past encounters. But as Venom shows his more caring side in the adoption, Peter would start to trust him a bit. They'd have to learn to communicate, which would be difficult because of Venom's different way of thinking.
In some fanfictions, Peter's death might be a result of a long - term consequence of his superhero activities. For example, the constant use of his powers could have weakened his body over time, leading to a tragic end. It could also be that a new and unexpected enemy emerges, one that he underestimates and this ultimately costs him his life. The death then serves as a shock factor to drive the story forward, perhaps leading other characters to avenge him.
One interesting plotline could be Peter Parker struggling to control the Anti - Venom symbiote. Maybe it has a mind of its own and tries to take over Peter's actions at times. For example, it might lash out at his enemies more brutally than he intends.
In a fanfiction where Peter Parker becomes Venom, it could be due to a scientific experiment gone wrong. Maybe Oscorp was working on a new symbiote project, and Peter, being the curious and heroic type, gets involved accidentally. The transformation would change his personality, making him more aggressive at first as he struggles to control the new power. He might initially see the symbiote as a curse but later learn to use it for good, in a different way than he does with his Spider - powers.