What differnt kind of beasts do they talk about? How is the beast revealed to us by the author?

The boys discuss monsters in the classic sense. Ralph repeats the rule that the only place where they will have a fire is on the mountain. Addressing the spreading fear among the littluns, Ralph then attempts to demystify the question of the "beastie" or monster. He admits that he is frightened himself, but their fear is unfounded. Ralph again assures the group that there are no monsters on the island.The assembly highlights how fear ferments and spreads in a group. The littluns begin with a concrete example of a frightening incident that is easily explained and is understandable, but the idea of something more sinister on the island provokes mass hysteria. The terrors that the boys imagine become progressively more abstract and threatening. Percival uses concrete facts about squids to arrive at an illogical conclusion that a squid may emerge from the sea to harm them. This then provokes the unfounded rumors that there may be supernatural beings, ghosts, on the island.

Monsters, violent squid, and ghosts: all three creatures represent different instantiations of the "beast" or "beastie" that has been the subject of the boys' mounting fear.