Yoshi's Story

Unlock Black Yoshi

On level 2-1, find the tulip that turns you into an egg and shoot yourself upward. You will land on a platform with a bubble, so pop it and get the black egg. Complete the level without dying to unlock Black Yoshi.
On level 2-2, go through the level to the tulips. To the left of Miss Warp there will be a tulip, eat it. Fire yourself upward and break out near the ceiling. Shoot the bubble and collect the black egg, then beat the level without dying to unlock Black Yoshi.
On level 2-3, find the Help Box that hints about a big egg. From there go left and jump on the final floating rock. Jump on the floating rock above that, and shoot the ? bubble with your eggs to get the black egg. Finish the level without dying to get Black Yoshi.
On level 2-4, go through a couple of rooms until you get to the room with vines/snakes in it, and go all the way to the right to get the black egg. Finish the level without dying to unlock Black Yoshi.

Unlock White Yoshi

On level 3-2, go through the level until you find Miss Warp 2. Go up the stair platforms and further left. At the end you'll see the bubble. Pop it, get the egg, and finish the level without dying to unlock White Yoshi.
On level 3-3, go through the level. When you reach the screen that has the dog on it next to a red pipe you can't get to. Go down the next red pipe and you'll find the bubble the egg hides in. Pop it, grab the white egg, and finish the level without dying to unlock White Yoshi.

White Shy Guys

These White Shy Guys, if you find one, will bring back one of your dead Yoshis. Note: If you have no dead Yoshis, there won't be a White Shy Guy.
In level 1-1, find and then go left of the second heart. The Shy Guy is in the bubble.
In level 1-2, find and then go right of Miss Warp 3. The Shy Guy is in the mystery crate.
In level 1-3, go right from the melon delivery. The Shy Guy is in a bubble.
In level 1-4, go past the umbrella. After that go down until you come to five blocks. Shoot the one farthest to the left.
In level 2-1, go down the first vase. After you have gone down it, there should be a wall of blue rocks. Blow out all the rocks and then you come to blue rocks on the ground. The one on the bottom holds the White Shy Guy.
In level 3-3, go through the level until you come to a fork in the path and each path is leading to a different vase. Go down the path that has the dog on it, and go down the vase that the dog is near. When you come out you should be on a path that has two question mark boxes. Ground pound on the first box and you will have the White Shy Guy.
In level 4-1, look around for four blue rocks. Hit the upper left rock with an egg, and the White Shy Guy will be yours.

Kill Yourself

Why would you want to kill yourself? Perhaps you picked Yellow Yoshi and wanted Green... But whatever reason you should do it, all you have to do is press Z, L, A, and B buttons at the same time.

Break Bubbles

Did you find a bubble with an item you really, really wanted in it, only to discover you have no eggs? Not a problem. All you have to do is run into/jump on/ground pound on the bubble over and over, and eventually it will pop.

Mario Paint Song

Go into Trial Mode, and wait for the song to finish playing eight times. After that, the Mario Paint music will play.

Heart Fruit Message

If you eat a Heart Fruit, a letter will appear. If you eat all of them in the game, it will spell out You are Yoshi's great partner.