A ? Block, known as Mystery Block in Super Mario Land and Prize Block in Super Mario World, is a common type of block in the Mario series.
A ? Block is more likely to contain a coin instead of an item. Sometimes a ? Block doesn't even contain a coin, nor an item. A ? Block first appeared in Super Mario Bros., and have appeared in most of the Super Mario games, excluding Super Mario Bros. 2, Super Mario 64, Super Mario Sunshine, and the Super Mario Galaxy series. ? Blocks should not be confused with ! Blocks.
In Super Mario series, the ? Blocks give Mario coins and useful items, like Super Mushrooms, for example. Some ? Blocks are invisible, the player can find it when is jumping and accidentally hits it. They can release Beanstalks, making it available for climbing.
In Super Mario Bros.: The Lost Levels, the ? Block can contain Poison Mushrooms, an item that introduced in this game.
In Super Mario Galaxy and Super Mario Galaxy 2, the block can give the player Star Bits.