First Appearance

Captain Toad: Treasure Tracker

Effect on Player

Most likely unlocks secret levels when a certain number of diamonds are collected
Diamonds are collectible items in the upcoming game Captain Toad: Treasure Tracker. They serve the same purpose as Green Stars in Super Mario 3D World and Star Coins in the New Super Mario Bros. series and Super Mario 3D Land and like said games, they are scattered around on the stage, and sometimes a certain puzzle must be done to collect them. Not much is known about them at this time.