Simplify the following text for a Grade 10 native English-speaking person.
Original: Their survival is immediately threatened by a number of mysterious entities , including polar bears , an unseen creature that roams the jungle ( the `` Monster '' ) , and the island 's malevolent , and largely unseen , inhabitants , known as `` the Others '' , occurring throughout the whole first season .
Simplified: The survivors find mysterious things including polar bears , an unseen monster , and the other people living on the island , known as the `` Others . ''