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.
One option is that it could be a corrupted version of one of Max's friends. For instance, if someone was influenced by the dark forces at play in Arcadia Bay, like the vortex that was causing all the chaos. Maybe they are being controlled and don't even realize that they are the one shooting Max. It could also be a member of a secret organization that has been observing Max's powers from the shadows and decides that she's too dangerous to be left alive, so they send an assassin to shoot her.
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.
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.
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.
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.
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.
One possible scenario could be that Max uses her time - rewinding ability right before getting shot to avoid it completely. Maybe she sees the shooter in advance and manages to either stop the shooter or change the situation so that the shooting doesn't occur. Another scenario could be that she gets shot but somehow her powers are affected in a new and unexpected way, like she starts seeing visions of the future related to who shot her and why. Or perhaps she gets shot and Chloe is able to get her to a hospital in time, and while Max is in a coma, she has strange time - traveling dreams that give her clues about how to prevent the shooting from really happening.
It could be Nathan Prescott. He has shown signs of instability and aggression in the game. Maybe he wants to get revenge on Max for interfering in his life or for making him look bad. He could be desperate enough to kidnap her.