New Super Mario Bros. 5-Star Adventure 2
Tap-Blocks debut in this game's Assist Mode. At first, they appear clear on the GamePad and don't appear on the TV screen at all. When the Assist Mode player taps the block, it appears on the TV screen for a short time. The block can be tapped again to make it reappear if it vanishes.
New Super Mario World
In New Super Mario World, Tap-Blocks appear with a similar purpose but a different implementation. They now appear as black and white versions of Question Blocks and Brick Blocks, and will only exist if someone is using the Boost playstyle.
Black Tap-Blocks first only appear to a Boost player, in translucent form. They can be tapped to make them visible on everyone's screens, at which point any other player can open it. Similarly, white Tap-Blocks appear translucent on non-Boost players' screens at first. Hitting it will make it visible on the Boost player's screen so that they can tap it to open it.