It could be a lone wolf type of character. This person is a survivor in the same world as Clementine but has gone a bit crazy from all the hardships. They see Clementine as a competitor for resources and decides to shoot her to get rid of the competition.
Perhaps there's a power - hungry leader in a nearby settlement. Clementine's actions or presence pose a threat to their control. They send one of their henchmen to shoot Clementine to send a message to her group or to simply eliminate a potential problem.
Maybe Clementine is in a situation where there's a misunderstanding. She's in a new community and some people think she's a threat. A panicked person shoots her. Then the story could focus on how she tries to convince the community she's not a danger while also dealing with her injury and trying to survive.
Dr. Eggman could be the antagonist. He's always trying to defeat Sonic, and shooting him could be part of one of his evil plans. Maybe he developed a new weapon specifically designed to take Sonic down.
It could be a rogue agent from their own organization. Maybe someone who has a grudge against Washington for some past event. This person might see Wash as a threat to their own plans and decides to take him out.
In a more complex plot, Clementine might be betrayed by someone she thought was an ally. They shoot her and leave her for dead. But she survives and has to seek revenge while also dealing with her injury. This could involve her finding new allies and learning who she can really trust in this harsh post - apocalyptic world. She may have to face her own mortality and become even stronger in the process.
Perhaps a mysterious stranger who has some unknown vendetta against the Heartland family. This person could have been lurking around the ranch for a while, waiting for the perfect opportunity to strike. Or it could be someone within the community who has a hidden agenda and sees Amy as an obstacle to their plans.
Lee would be devastated if he were still alive. He would do everything in his power to save her, like searching for a doctor or medicine. He would be by her side constantly, giving her words of encouragement.
It could be a new group of survivors who are extremely territorial. They see Rick's group and Clementine as threats to their resources. This group might be led by a power - hungry man who is willing to do anything to protect what he thinks is his, including attacking Rick's group and trying to capture Clementine.
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.