The ocean is a large body of water.
Small fish such as Clownfish and Urchins.
Dolphins - Green MOBs that can scare away Sharks.
Great White Sharks
Megalodon - The Giant Shark, this is a giant mini boss that spawns in deeper waters.
Tentacolon - The Giant Squid, this is a giant mini boss that spawns in deeper waters. It has the most health compared to any other mob in the game. Though, it doesn't do to much damage.
Atlantis can be found in -200 waters. It is a rare, dome-like city that houses the elusive Visitors. It is recommended to use a Diving Suit before visiting such a location.