While you explore the world of Mario & Luigi: Brothership, you’ll run into Issa Rock, a young girl with a thirst for knowledge. As you explore the islands, you’ll find all sorts of side-quests, secrets, and more, but you can only find Hidden Reefs out in the open ocean. These Reefs are found all around the seas of Concordia, so you have some work ahead of you before you can find them all.