The creature depicted in this image is a cyclops. The cyclops is a giant monster with one eye in the middle of its forehead. One of the main antagonists in this book. The cyclops is naturally hostile because it doesn't want anything to do with travelers, so that is why it acts in such a hostile manner. Polyphemus is a cyclops. Polyphemus is definitely a hostile character because he stole the fleece from heroes and ever since, countless satyrs have come to the island to reclaim it, but Polyphemus just eats them and thinks nothing of it.
Image Website: http://www.varietyportal.com/cyclops/
Image Website: http://www.varietyportal.com/cyclops/
This is Riptide. Riptide is the sword that Percy used throughout both The Sea of Monsters and The Lightning Thief. Like most mythological creatures, this sword has a disguise that makes it look like a completely normal object. When it is not in use, Percy has it disguised as a regular ballpoint pen. Percy brings this blade everywhere he goes so he always has some protection. This is Percy's signature weapon. He has fought many fights with this weapon.
Image Website: http://camphalfblood.wikia.com/wiki/File:Sword-Riptide.jpg
Image Website: http://camphalfblood.wikia.com/wiki/File:Sword-Riptide.jpg
The thing that this image shows Clarisse carrying is the Golden Fleece. This is the main goal of the adventure that Percy and his friends went on. The Fleece had the power to heal Thalia's Tree, which would restore the boundaries that blocked the evil monsters from coming inside the camp. They had to steal the fleece from Polyphemus, while they were trying to steal Grover back. After the tree is healed, the camp counselors put the fleece in a place where no one can get to it that is not a demigod.
Image Website: http://camphalfblood.wikia.com/wiki/The_Golden_Fleece
Image Website: http://camphalfblood.wikia.com/wiki/The_Golden_Fleece
The mysterious creature depicted in this picture is a Hippocampus. It is a horse that lives in the ocean. The hippocampi helped Percy and his friends on their quest multiple times. In the beginning, the hippocampi brought Percy and his friends to the cruise ship that would bring them slightly closer to their goal. After they had escaped from Polyphemus, they had no way to get back to the United States, but that was when the hippocampi came back. The hippocampi brought everyone back to Florida safely, and Percy and his friends would not have gotten back alive if it weren't for the hippocampi.