Supreme Court Mandatory Appellate Jurisdiction Reform Act of 1984 - Repeals the provision of the judicial code authorizing any party (in a proceeding to which the United States is a party) to appeal directly to the Supreme Court from a Federal court order which declares an Act of Congress unconstitutional. Repeals Supreme Court mandatory jurisdiction to hear appeals from a Federal appellate court decision holding a State statute unconstitutional. Repeals Supreme Court mandatory jurisdiction to hear appeals from decisions of the highest court of a State (including Puerto Rico) which hold that: (1) a Federal treaty or statute is invalid; or (2) a State law is valid.