Super Mario Advance/Yoshi's Challenge

After you complete the Super Mario Bros. 2 portion of Super Mario Advance, a new variation of the game becomes available. This is known as Yoshi's Challenge. In Yoshi's Challenge, two eggs are hidden in the Sub-space of each level, for a total of 40 eggs. While they are usually found in similar places as the mushrooms, they're often not in the exact same locations, so you must do some hunting, even if you know precisely where all of the mushrooms are.

In addition to the challenge of finding these eggs, you must do so without dying. If you die during the level, any eggs that you have found will be lost. You can collect them once again after you die, but you will only get credit for finding eggs as long as you complete the stage you found them in. Contrary to popular belief, you are not required to find both eggs in one run. You can find one egg and complete the stage to get credit for that egg, and then return to the stage to find the second egg at a later time.

A couple of things to note about Yoshi's Challenge:
 * Your saved score will continue to accumulate as you play through Yoshi's Challenge.
 * Your remaining lives will similarly be recorded, whether they increase or decrease.
 * You can choose any stage, and collect the eggs in any order that you like.
 * You are not required to find all 100 A-coins in order to unlock the challenge.
 * You can collect any missing A-coins along the way, but it is recommended that you do not focus on finding A-coins as they can cause you to take some unnecessary risks, and potentially lose any eggs you found.
 * The eggs will replace two of the mushrooms. As a result, the most number of health units you can possess in any one level is three; the two you start with and one mushroom if one is available in the stage.  Most, but not all stages have one mushroom in Yoshi's Challenge.
 * As stated above, you must collect any eggs and complete the stage, including defeating any bosses, in order to earn credit for finding an egg.

Perfect completion
Every time you obtain a complete set of egg for each world (six in most case, except for World 7 which only has four), the eggs will hatch into baby Yoshis which quickly grow to full-sized Yoshis. Once you have collected all four Yoshis, you will receive the "PERFECT" screen shown to the left. After you accomplish this, a full-grown Yoshi will replace the Yoshi egg that was added to the lower right corner of the title screen. (Note that the change in sky color from blue to tan is a function of finding all 110 A-coins.)