The letter "p"

"And making me guard the name's stupid missing letter...No way to treat a parrot!"

- Parrot



P is a special item in the game Paper Mario: The Thousand-Year Door.

Mario and Vivian needed the letter P to guess Doopliss's name, because while guessing his name, their letter options lacked this letter. This was also a very clever way to prevent people from cheating (by looking up Doopliss's name on sources such as player's guides and the internet). Also, it forces players who have already played through the game, and who know his real name, to do the chapter properly - and not to be able to skip a large chunk of it. Although a capital "P" is always available when Doopliss prompts Mario and Vivian to guess his name, using it won't work, for the spelling must be case sensitive.

To find the letter, Mario is forced to use Vivian to access a secret portion under the well in Creepy Steeple, using her Veil power. There, Mario can roll up into a tube and access a treasure room, where one of the chests contains the letter. By using Veil again, a parrot in the room reveals Doopliss's name for the player.

Trivia

 * Doopliss is called "Rumpel" (ランペル Ranperu) in Japan. The missing letter in the Japanese version is ン ("n" in the katakana syllabary) rather than the English "p". In other languages, where Doopliss is called "Rumpel" or "Rampel", the p is also the missing letter.