Dotted Line Block
From the Super Mario Wiki
Dotted Line Blocks are transparent objects found in several Mario games such as Super Mario World, Super Mario World 2: Yoshi's Island, Yoshi's Island: Super Mario Advance 3, Yoshi's Island DS and New Super Mario Bros. Wii. In Super Mario World, they come in four colors and turn into ! Blocks once the player hits the ! Switch in the Switch Palace of the corresponding color. In both Yoshi's Island games, after hitting a nearby ! Switch, the Dotted Line Blocks will temporarily become solid and are able to be used as platforms. Dotted Line Blocks in New Super Mario Bros. Wii become Red Switch Blocks after pressing the red ! Switch in World 3.
Transparent boxes similar to Dotted Line Blocks appear in Super Mario 64 and its remake Super Mario 64 DS, where they turn solid and are able to be used after hitting the ? Switch in the level "Tower of the Wing Cap."
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