A Credit Card may seem out of place in Angel Land, but Pit's not going to argue. This handy item, only obtainable in Treasure Chambers by outsmarting the God of Poverty, allows Pit to purchase items from a Black Marketeer. It works slightly different in the two games it appears in.
If Pit has this in his inventory while not having enough Hearts to purchase an item from the Black Marketeer, and he collects the item, his Heart total will be reduced to 0 and the rest will be placed as debit on the card. Until he collects enough Hearts to equal out the balance, nothing more will be added to his total and Pit will be unable to buy anything else until the debt is paid off.
