1UP Kinoko ga 3UP Moon ni kawaru!

The Blue Switch is a Japan-exclusive e-Reader card for use with Super Mario Advance 4: Super Mario Bros. 3. It was released in Series 1 in Japan.

Once it is scanned, all of the 1-Up Mushrooms in the game become 3-Up Moons. This feature allows Mario and Luigi to accumulate extra lives more easily.

Japanese
1UPキノコが3UPムーンに変わる!

Translation
1-Up Mushrooms turn into 3-Up Moons!