Since I don't know the story, I can only guess. There must be the little green monster itself. Maybe there are other friendly or unfriendly creatures that it interacts with, like a wise old owl or a mischievous little rabbit.
I'm not sure since I haven't read the story. But it could be a story about two friends, where one becomes jealous of the other's success.
Well, in a general 'a green monster story', the main character would be the green monster. There might also be some side characters like the monster's family if it has one in the story. And perhaps a brave hero or heroine who tries to understand the monster instead of being afraid of it. There could also be a villain who wants to capture or harm the green monster for some reason.
The plot could involve the little green monster's discovery of its own identity. Maybe it starts out not knowing where it came from or what it's capable of. As the story progresses, it could learn about its unique powers or characteristics that set it apart from others in its world. It might also encounter some sort of conflict, like being misunderstood by the other characters in the story because of its appearance as a green monster.
There could be many possible main characters. It might be a woman, let's call her Alice, who is the one consumed by the 'green - eyed monster' of jealousy. She could be jealous of her best friend's new boyfriend. And her best friend, say, Lucy, would also be a main character as the object of the jealousy. Maybe there's also an old wise neighbor, Mr. Brown, who tries to give Alice advice on how to overcome her jealousy.
Since we don't know the exact 'green - eyed monster story', the main characters could be many different types of people. It might be a group of students in a school setting. One student, perhaps not as popular or not as good at studies as another, could be the main character who is filled with jealousy (the green - eyed monster). Or it could be two co - workers competing for a project, and the one who is jealous of the other's skills or advantages becomes the central figure in this story of envy.
Obviously, the little green pig is one of the main characters. It's the one that the story is centered around.
Since I don't know the story, I can only guess. The main character is surely the little green dinosaur. There might also be other dinosaurs, like its parents or siblings.
There might be other animals too. For instance, a wise old owl could be another main character. The owl could give advice to the little green snake or help it out in some situations. And perhaps a friendly squirrel that befriends the snake and they have adventures together.
Since I don't know the story, it could be the owner of the little green tractor. Maybe it's a farmer.
There could be a group of villagers. They are the ones who are afraid of the big green monster. And perhaps there is a wise old man among them who gives advice on how to deal with the monster.