Hidden Coin

Hidden Coins (also known as Dash Coins ) are special types of coins that have been seen in the New Super Mario Bros. games, Yoshi's New Island and Super Mario Run. Hidden Coins are somewhat rare, and only appear in a few levels.

Description
Hidden Coins first appear as an outline of a Coin; if Mario or another character passes through the outline, it will then turn into a regular coin after a moment. In New Super Mario Bros. Wii and New Super Mario Bros. U, the coins appear with a quieter sound effect once passed through.

In Super Mario Run, Hidden Coins make their first appearance in Ghost-Door Deception. This time, they appear more commonly than in New Super Mario Bros. Wii. Touching one can reveal a regular Coin, a Pink Coin, a Purple Coin, or a Black Coin, depending on the level.