Crystal Ball

Crystal Balls are items featured in many games throughout the Mario franchise.

Super Mario Bros. 2
Crystal Balls are first seen in Yume Kōjō: Doki Doki Panic and its update, Super Mario Bros. 2, where it gains an animated red line. They are found at the end of most levels. Picking one up will open the Mask Gate and allow the player to proceed to the next level, while in boss levels, they allow the player to face the world's boss. They are usually guarded by Birdo. In the NES version of Super Mario Bros. 2, Birdo can be seen holding the Crystal Ball in front of her during battle. In later versions, it seems to come out of her snout upon defeat.

Paper Mario series
They are seen in Paper Mario as the main magic tool for Merlon's family. There is an Ultra Stone variant. It is also seen with Merlon in Paper Mario: The Thousand-Year Door.

In Super Paper Mario, when Chapter 5 is complete, the player can go see Merlee at Flopside. She claims that she wants a Crystal Ball from Merluvlee, and wishes the player to go get it for her. After doing the task, Merlee rewards the player with a free charm and a key that opened a storehouse containing Piccolo the Pixl.

Luigi's Mansion
In Luigi's Mansion, Madame Clairvoya uses a Crystal Ball to see into the future. To make her appear, Luigi must continuously shine his light onto the Crystal Ball to cause it to light up with a pitch-increasing shimmering noise, eventually ending once she appears.