Mold is the most obnoxious thing of all time. Moldy bagel? Moldy Gouda? Throw it out. Moldy uppermost corner of your room? You have to pay a man major dollar bills to strip the problem area, and probably the whole wall (paying for preventative labor is like paying for antibiotics to maybe work.) Mold in your apartment is a serious risk. According to DOB laws, New York City must follow Department of Health guidelines for indoor air quality. So show your landlord photos of the mold wad and make sure he does something about it immediately.