New Super Mario Bros. Cheats

99 Lives In Two Worlds
World 7-5-Three quarters way into the map, on the down slope between the two bullet towers, there is a green turtle and a small bomb minion. Stomp on the green turtle and have it bounce between the two towers, it will knock the lower bullets for 1-ups. Make sure to jump over the turtle each time it passes underneath, and watch out for overhead bullets!

World 2-4, right at end climbing up to flagpole, the exact same way as the very 1st Super Mario for NES. Stomp as regular mario onto the descending turtle as it is falling onto the brick above you. Mario will then jump repeatedly on that turlte for a quick 1UP every half second.