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.
File:Super Mario Advance Yoshi 1-1a.png The first Yoshi egg is close to where you find the first Mushroom, except that it's on the ground on the opposite side of the vine.
File:Super Mario Advance Yoshi 2-1a.png Borrowing from a trick you learned in World 6-1, you'll need to rescue this egg before it sinks too low in the sand.
File:Super Mario Advance Yoshi 2-1b.png Grab the potion from beneath the grass that's found behind the pyramid, and bring it back to the Panser to find the second egg.
File:Super Mario Advance Yoshi 2-2a.png In the small enclosure where you found one of the Mushrooms, pick up the potion and bring it all the way back to the right side to find an egg.
File:Super Mario Advance Yoshi 2-2b.png A newly added Mushroom saw you bring a potion half-way up the sand. To find the egg, you'll need to bring that potion all the way to the top.
File:Super Mario Advance Yoshi 2-3a.png This egg is even closer to the location of the potion than the Mushroom that you originally used to collect with it.
File:Super Mario Advance Yoshi 2-3b.png After stepping inside and falling, be sure to stop on this center platform. Simply drop the potion right where you collect it to find the egg.
File:Super Mario Advance Yoshi 3-1b.png To find the second egg, search the cloud above the very narrow hill that's close to the fire breathing Panser plant.
File:Super Mario Advance Yoshi 3-2a.png From the start, run all the way to the right, and then blast a hole in the floor before grabbing the potion and tossing it on the floor.
File:Super Mario Advance Yoshi 3-2b.png Look for this egg in a very similar spot to where you found the second Mushroom. Only this time, check the left chamber instead of the right.
File:Super Mario Advance Yoshi 3-3b.png Super Mario Advance added a potion at the top of a set of ladders in the middle of the tower. Grab the potion and use it at the bottom of those ladders to find an egg.
File:Super Mario Advance Yoshi 4-1a.png Don't slide too far away from where you collected the potion. Look to the right to find the egg, instead of to the left where you found the Mushroom.
File:Super Mario Advance Yoshi 4-2b.png Similarly, the second egg is pretty close to where the newly added third Mushroom is located. Just pick up the potion in between the whales, and drop it.
File:Super Mario Advance Yoshi 4-3a.png The first egg is positioned right where you found the first Mushroom. However, eggs are a little taller than Mushrooms so you may need to use a power-jump.
File:Super Mario Advance Yoshi 4-3b.png Like the second Mushroom, this egg is found on one of the turrets at the edge of the tower. Unlike the Mushroom, the egg is found on the left side.
File:Super Mario Advance Yoshi 5-1a.png Similar to how you found the newly added Mushroom in the middle of the waterfall section, you'll find the egg up on the higher platform.
File:Super Mario Advance Yoshi 5-1b.png To get this egg, you must be familiar with the method to collect the second Mushroom at the end of the stage. Only instead of removing the right Mushroom Block, you must remove the left one.
File:Super Mario Advance Yoshi 5-2a.png Look for the first egg right near the dangerous Panser plant between the two Hoopsters. Remember that the Panser plant now sits on top of a potion.
File:Super Mario Advance Yoshi 5-2b.png Once you collect the potion from underneath one of the Snifits on the right side, you must get a lift from Hoopsters in order to reach the top where the egg can be found.
File:Super Mario Advance Yoshi 5-3a.png Instead of finding the first Mushroom just to the left of where you collect the potion, you'll find the first egg just to the right.
File:Super Mario Advance Yoshi 5-3b.png After climbing down the ladder, use the Bob-ombs to blast a hole to the ground below, grab the potion, and make sure you can access the ground above in order to collect the egg.
File:Super Mario Advance Yoshi 6-1a.png Just like you did with the first Mushroom in this world, you'll have to rescue the egg from the quicksand. Only this time, you must look to the left.
File:Super Mario Advance Yoshi 6-1b.png You'll find the second egg among the row of jars set up inside the cave just before the boss. Use the potion found above the exit door.
File:Super Mario Advance Yoshi 6-2a.png There isn't a whole lot of land for the eggs to hide in this stage. The first egg is right next to the middle platform with the potion.
File:Super Mario Advance Yoshi 6-2b.png You'll need to grab the potion a second time from the center platform, and carry it all the way to the end. Drop it off near the exit to find the second mushroom.
File:Super Mario Advance Yoshi 6-3a.png Whereas the first Mushroom sat atop one of these short cactus plants, the egg will fall directly between them and start sinking in the quicksand if you don't rescue it.
File:Super Mario Advance Yoshi 6-3b.png The second egg is in the same location as the newly added hidden Mushroom. Explore the jar, grab the potion, exit the jar, and use it as soon as you return.
File:Super Mario Advance Yoshi 7-1a.png Rather than finding the first Mushroom on the grassy hilltop, you'll find it closer to the potion on the bridge. Just watch out for the Bob-ombs.
File:Super Mario Advance Yoshi 7-1b.png Grab the potion just below the door that leads to the boss. Instead of dropping down with it to find a new Mushroom, stay right there to find the second egg.
File:Super Mario Advance Yoshi 7-2a.png World 7-2 is the one world where you won't have to do much thinking. The first egg is right near where you found one of the Mushrooms.
File:Super Mario Advance Yoshi 7-2b.png The second egg is pretty close too. You just have to drop the potion a bit more to the right, in order to find this egg which is higher up on the ledge.
Every time you obtain a complete set of egg for each world (six in most cases, 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 100 A-coins.)
