Crystal Ball
Crystal Balls are items that have been featured in many games throughout the Mario series. They are first seen in Doki Doki Panic and its remake, Super Mario Bros. 2. They are found at the end of most levels. Picking one up will open the Hawkmouth and allow the player to proceed to the next level. They are usually guarded by a Birdo.
They are seen in Paper Mario as the main magic tool for Merlon's family. It is also seen with Merlon in Paper Mario: The Thousand-Year Door.
Madame Clairvoya uses one to see the future and other things in Luigi's Mansion. Another is used in Mario Party 6, in the Seer Terror minigame. Bowser uses it to see a player's "future," which usually is something bad. Occasionally, however, the player receives Coins or a Mushroom.
In Super Paper Mario, when Chapter 5 is complete, players can go see Merlee at Flopside. She claims that she wants her Crystal Ball back from Merluvlee, and wishes the player to go get it for her. After doing the task, Merlee rewarded the player with a key that opened a storehouse containing Piccolo the Pixl.