"Unfortunately, this won't map out your life." -AviDescription: Upon obtaining this item, a GUI will permanently appear on your screen. While you're in a dungeon, you'll see every individual room and it's number. It's only found in the dungeon rarely, and is purchasable in a dungeon shop for 8 coins. Fun fact: Every dungeon has out with 8 rooms, then 10 rooms, and finally 12 rooms with a boss door at the end.
What this item looks like in-game.