Hidden Block

Hidden Blocks (also called Invisible Blocks) are ? Blocks that are invisible to players unless they hit the block. Hidden Blocks first appeared after the fourth pipe in World 1-1 in Super Mario Bros., which contained a 1-Up Mushroom. Hidden Blocks did not have an appearance as when hit, they turned into Used Blocks.

Super Mario RPG: Legend of the Seven Stars
In Super Mario RPG: Legend of the Seven Stars, Surprise Boxes are invisible Treasure Boxes that contain various items from Frog Coins, Flowers, powerful healing items, and items used in battle. When Mario jumps at a spot where a Surprise Box is, it first reveals itself, and jumping at the revealed Surprise Box allows Mario to collect its contents. There are 39 Surprise Boxes in the game.

Paper Mario
In Paper Mario, the player may come across Hidden Blocks containing coins, healing items, badges, and other items, while some are also used as stepping stones to reach other areas. Such blocks can be found by using Watt's field ability. There are 47 Hidden Blocks in the game.

Paper Mario: The Thousand Year Door
Hidden Blocks function the same way in Paper Mario: The Thousand Year Door. The player can use Ms. Mowz's field ability to find them. There are 15 Hidden Blocks in the game.

Mario & Luigi: Superstar Saga
Hidden Blocks appear in Mario & Luigi: Superstar Saga, containing the elusive Hoo Beans. Such blocks are found by jumping around at suspicious platforms or patterns, or in seemingly "empty" dead ends. There are 42 Hidden Blocks in the game.

Mario & Luigi: Bowser's Inside Story
Hidden Blocks appear in Mario & Luigi: Bowser's Inside Story in Peach's Castle Garden, containing the last three Attack Pieces of the Special Attack, Falling Star.

Super Mario Maker
In Super Mario Maker, Hidden Blocks were given a sprite for use in Create mode, and as a partially-transparent grey ? Block.