P-Up, D-Down P is a badge in Paper Mario: The Thousand-Year Door.
Mario can use this badge to increase the attack power of his party members by one at the expense of their defense lowering by one. Mario can wear this badge by using two of his BP.
P-Up, D-Down P is found much later in the game. This badge is found in the Palace of Shadow, in the room before the room that follows a pattern and is the only way to proceed.