There were many types of legendary sea monsters. Some of the famous sea monsters included Bahamut, Cetus, the Kraken, Leviathan, and so on. Bahamut was a sea monster in Arabian mythology. It was shaped like a giant fish and carried a ruby mountain on its back. Cetus was a sea monster from Greek mythology. It had the body of a dolphin, the tail of a fish, and the head of a dog. The Kraken was a sea monster in Norway folklore and often appeared in European and American literature. Leviathan was a sea monster that symbolized evil in ancient legends and was usually described as a whale. Other than these sea monsters, there were also some other sea monster legends, such as mirages and water monsters.
It's likely about the adventures in the Sea of Thieves world. It might feature pirates, their quests for treasure, battles on the high seas, and the various strange and dangerous creatures that inhabit that world.
Yes, in a sense. Other players might take credit for things you've done in the game, like finding a valuable treasure or completing a difficult quest first. They could brag about it as if it were their own accomplishment, which is like stealing your story.