It could be a new villain, someone who has a personal vendetta against Peter Parker. Maybe a criminal whose operations Spider - Man has disrupted one too many times.
Perhaps it's a rival superhero who has gone rogue. They could be jealous of Peter's popularity or have a different view on how to protect the city, leading them to take extreme measures like shooting him.
Another option is a mind - controlled character. Some super - villain might be controlling an innocent bystander to do their dirty work and shoot Peter. This would add an interesting layer of complexity as Peter would have to deal with the fact that the shooter isn't truly at fault.
It could be a jealous rival detective who wants to get rid of Sherlock to gain more fame in the detective world.
It could be a dark wizard who has a vendetta against Fairy Tail. Maybe someone who Natsu defeated in the past and is now seeking revenge.
It could be a new villain who has a vendetta against Tony. Maybe this villain has some past connection to Tony that we don't know about yet, and they finally take their chance to harm him by shooting him.
It could be a former criminal that McGee helped put away. They might have escaped from prison and are seeking revenge on him for ruining their life.
Maybe it's a rival agent who is jealous of Booth's success and popularity within the agency. They might see shooting Booth as a way to get ahead in their career or gain more power within the organization.
There's also a possibility that it's an agent of a secret organization. This organization might be aiming to disrupt the hero society, and they see Bakugou as a key figure to target. So they send one of their best shooters to take him down.
There's also a possibility that it's someone who has a wrong idea about Conan. For example, a person who thinks Conan is involved in some sort of conspiracy against them or their family. This misunderstanding could lead them to shoot Conan in a moment of rage or fear, without really knowing who Conan truly is and what he stands for.
It could be a vengeful criminal that Spider - Man has put away in the past. This criminal has spent years in prison plotting his revenge and finally gets the chance when Peter is vulnerable. Maybe he manages to ambush Peter in an alleyway while he's on his way home from school or work.
It could be Nathan Prescott. He has a history of being unstable and involved in some dark things in the game. Maybe he has finally snapped completely and decides to target Max for some reason, perhaps because he feels she's getting in the way of his family's plans or because he blames her for his own problems. Another possibility is that it could be someone from the other side of the Arcadia Bay conflict, like a person who doesn't want the lighthouse to be saved and sees Max as the main obstacle to their plans.
It could be a jealous rival. Maybe someone who is envious of Peter's success or his relationship with a certain person.