The Golden Poo Snake may be found once you've obtained the Mechat. Defeating the foe requires having the Shoes of Hermes and Poo Bracelet. He can be found on the Southeastern Desert Island along with a treasure chest. It's recommended that you have each of your characters in your party eat garlic or obtain the "stink" debuff as this will assist in the Golden Poo Snake pursuing your party on the battle field.