From the Super Mario Wiki
This article is about the switch that appeared in Super Mario Bros. 3
. For information about the similar switch which appeared in Super Mario World
, see here
The Red Switch is an e-Reader card which is used with the game Super Mario Advance 4: Super Mario Bros. 3. It is only available in Japan.
Once this card is scanned on the e-Reader, it replaces all the enemies with more difficult ones. However, the points that the player receives from defeating these enemies are doubled, making the player's score accumulate much faster.