Blue Green Switch
From the Super Mario Wiki
The Blue Green Switch is an e-Reader card for use with Super Mario Advance 4: Super Mario Bros. 3. It was included in the Series 2 set of cards. Although technically a Power-Up card, it was labelled as a "Game Level" card.
Make vegetables sprout up in the level, then use them to attack enemies. This card can be used only in the existing game levels.