I'm not sure as you haven't told me the specific story. But it could be various actors or characters depending on the nature of the story. For example, if it's a horror story, it might be a well - known horror actor like Robert Englund if it's a Freddy Krueger - like monster.
We might expect the cast to bring the monster to life in a believable way. If it's a complex monster with a backstory, the actors would need to convey that through their performance. They could use body language, facial expressions and voice modulation to make the monster seem real. For example, if the monster is supposed to be menacing, the actor should be able to project that through their posture and the way they move. They also need to interact well with other characters in the story if there are any scenes where the monster confronts them.
The cast of Sea Monster 2020 included Kristen Stuart, Vincent Caso, T.J. Miller, John Gallagher, Li Meiqi, Zhang Yuenan, Sun Xun, Yu Kehong, and An Yanqing.
It could be the main character themselves. Sometimes, in a psychological thriller, the character discovers that they are the source of all the problems, and in a way, they are the monster.
The story in 'Cast of Monster High The Origin Story' is centered around the idea of these monsters creating their own world at Monster High. They come from different backgrounds - mummies, werewolves, vampires etc. The new arrival of Frankie Stein shakes things up a bit as she is different from the others in some ways. This leads to a series of events where they learn to accept each other, face their own insecurities, and build a community that is inclusive of all their differences.
Well, it could be a symbol of fear or the final challenge in the story. Maybe it represents the unknown that the characters have been dreading all along.
The significance could be to create suspense. It makes the reader curious about what the monster actually is, whether it's a literal monster or a metaphor for something like a big problem or a character's inner fear.