You can get three crowns-worth of lives, or 1,110 lives, in World 1-2. You can do this by passing the first Koopa and making your way to the area with a second Koopa and a Goomba on a slightly raised platform. Kill the Goomba, then jump on the green Koopa and steal its shell. Hop up onto the platform with the Goomba and face the rear wall while standing in front of the three brick blocks (press the D-pad UP to aim directly at the wall). Throw the Koopa and then immediately jump. Don't press anything else and you will bounce off the Koopa shell and never touch the ground while it bounces infinitely off the rear wall. This will result in infinite 1-Ups so long as you don't move! You'll need to return to the level twice to fill up your lives to 1,110 because the time will run out once you hit 600 or so on your first go.
Alternate method: You can get more lives (about 900) if you toss the first shell through the pipe, so that it bounces back and forth on the lip of the lower pipe. As long as you are facing the right direction (East/West) the shell will bounce back and forth very fast.
