Secret Door

Secret Doors are a type of stickers found in Paper Mario: Sticker Star. They are located exclusively at Outlook Point and sell for 80 coins. Their main purpose is to be Paperized onto silhouettes of doors found mainly on walls to see what is behind, usually several powerful stickers or a Thing. They can also be used to successfully escape a battle by having a door appear and have Mario walk through.

Trivia

 * A Secret Door is only found outside of Outlook Point twice; in Ice Flow after Mario reveals several Hidden Blocks, and in Bowser's Snow Fort after Mario defeats the two Shy Guys holding the Traveling Toad hostage.