Super Mario Advance 4: Super Mario Bros. 3 features e-Reader compatibility, in that it can link up to a second Game Boy Advance with an e-Reader. Upon scanning in one of three types of cards, something will then be triggered in the game. One type of card present in the game are the Switch Cards. These cards had a significant effect on gameplay, in that they generally made massive changes to the game when used. Out of the seven released Switch Cards, only two of them were released outside of Japan. Additionally, unlike the e-Reader levels, these features were left out of the games re-release in the Wii U Virtual Console. In total, there are fifteen switch effects, five of which are unused. Said effects also have unused pop-up icons that were supposed to appear on the Game Boy Advance screen when said effect was activated.
Switches released worldwide
- The Orange Switch, designated X2, when activated, made Fire Mario's fireballs turn non-boss enemies into coins, like in Super Mario World.
- The Blue Green Switch, designated X3, when activated, made grass with turnips appear throughout the main game, which Mario could pluck and throw at enemies, like in Super Mario Bros. 2. It is permanently on in World-e.
Switches released in Japan
- The blue switch, designated X1, when activated, changed most 1-Up Mushrooms in the game into 3-Up Moons, allowing the player to accumulate extra lives much faster.
- The yellow switch, designated X4, when activated, gave Luigi his scuttle ability from Super Mario Bros. 2 in the main game, and made his fireballs bounce higher, like in Super Mario World: Super Mario Advance 2. It is permanently on in World-e.
- The green switch, designated X5, when activated, caused every World-e level to have a slow timer countdown and music for the first 50 counts of the timer, giving the player more time to complete each level. Once this effect expires, a coin sound effect is played, and both the timer and the music go back to normal speed.
- The cyan switch, designated X6, when activated, cut the Power Meter in World-e from six steps into just three, making it much easier to run across stages and fly with Raccoon or Tanooki Mario.
- The red switch, designated X7, when activated, replaced most of the enemies in the game with more difficult ones, doubled any points gained and the bosses' health, and made Mario go directly from any fully powered-up form to Small Mario, rather than to Super Mario whenever he got hit, as in Super Mario Bros., Super Mario Bros.: The Lost Levels, and the original version of Super Mario World. In the game's code, these are four separate effects, meaning that through the use of a cheat device, one could activate one effect without activating the others.
Completely unused effects
- There was going to be an effect that caused point combos from defeating multiple enemies continuously would start at 4000 points. This would mean that the player would start earning extra lives starting from the third enemy.
- There was going to be an effect that caused any block that contained a 1-Up Mushroom to contain three 1-Up Mushrooms instead.
- There was going to be an effect that saved Mario the first two times he fell into a pit during a level. The first time, a two-block-wide platform would carry Mario back up; the second time, just one block would carry him. Afterwards, Mario would lose a life like usual.
- There was going to be an effect that dropped a random power-up during a level if Mario was hit by an enemy, similar to Super Mario World.
- There was going to be an effect that caused any recorded demos to show off Luigi instead of Mario.