Net Dolphin Madame(망돌마담, mang dol-madam, net dol-madame. Shortened from 망돌고래마담, mangdolgorae madam, net dolphin madame) is the Queen of the Net Dolphins. It likes to eat fish. The Net Dolphins gather fish for it when it calls. Baam and Rachel had to get inside it to pass the Submerged Fish Hunt Test. The average human can survive a journey through the Madame's digestive tract.
Notes and Trivia
Mangdol Madame is a mistranslation. "Mangdolgorae"(망돌고래): "mang" means "net", "dolgorae" means "dolphin". However, 고래(gorae) means whale. Dol(돌) means many things like "stone" and so on.
By adding dol(돌) to gorae(고래), the term "whale" becomes "dolphin"(dol-whale). And Ma-dam means Madame/Madam(마담). So, Net Dolphin Madame should be Net Dol-whale Madame (망돌고래마담).
However, the whale(고래) part is missing altogether, making it Net "Dol"-Madame(망돌마담).
Note from GoDai: The biggest problem is: what does "dol" mean in this case? So, SIU sorta made up this word Dol-Madame. By comparison, a Dol-Madame is to a Madame as a dolphin is to a whale. So in all technicality, Net Dolphin Madame is probably the correct translation, and SIU probably said the other nonsensical thing as a shortened form.