Adult Shine Block
From the Super Mario Wiki
Adult Shine Blocks are objects found in Mario & Luigi: Partners in Time. They are semi-rare blocks with a Shine Sprite symbol. These can only be hit by adult Mario and Luigi. An Adult Shine Block is always found near the entrance of a pitch-black room, which Baby Mario and Baby Luigi must enter by themselves. It is impossible to see the correct path through the room unless the Adult Shine Block is hit. If the Adult Shine Block is red, Mario has to hit it, while it is green, Luigi has to hit it. Once the block is hit by the correct brother, a Small Shine Block appears and floats over to the babies. When struck, this block illuminates the room for a short period of time, after which the light fades and the Adult Shine Block must be hit again. If the wrong brother hits the Shine Block, a Fireball can land on the babies, forcing them to restart the room from the entrance (although it can be avoided).