The biggest creature in Subnautica is the Sea Emperor Leviathan. This massive leviathan is the largest known creature in the game, and is truly a sight to behold. Measuring in at an impressive 30 meters long, this behemoth is not to be taken lightly. The Sea Emperor Leviathan is a slow moving but powerful creature that can easily crush anything in its path. While it may not be the fastest or most agile creature in Subnautica, its sheer size and strength make it more than a match for any other creature in the game.