What is a Yoshi Egg challenge in "Mario Brothers"?

Yoshi's Egg Challenge is a variation of gameplay in the "Super Mario Bros. 2" sequence of "Super Mario Advance." This challenge is only available after the game has been played through once.

The goal of Yoshi's Challenge is to find the two Yoshi eggs hidden on every level, usually hiding in mushroom blocks, for a total of 40 eggs. In order to collect an egg successfully, the player must navigate through each level without dying. If the player dies, the eggs from that level must be recollected. After every set of eggs is found in each world, the Yoshi eggs hatch and become full-grown with every egg the player finds.