Here's a way to instantly kill your Yoshi (we don't know why you'd want to, but perhaps if you get stuck somewhere). Press the Z, L, A and B buttons at the same time and your Yoshi should die no matter how many health petals he has.
In the level "Piranha Groove" (4-4), get shrunk. Then while small, hit an egg block. It will produce an extemely small egg. Pick it up when your still small. When you regain nomal size the egg will stay tiny. But don't worry, a tiny egg still packs the same wallop as a nomal one.
Keep White and Black Yoshi
If you get any of the black or white Yoshis (you can only have one of each), and beat the game, when the book flips to the last page, it shows the black or white Yoshi in addition to the rest of the Yoshis. Also now, whenever you start a new story, you start off the with the black and white Yoshi. (Both of these only work if the Black and White Yoshis are alive when you beat the game.
Unlimited Continues Trick
Want to be on the same page if you lose all your Yoshis? When you lose your last life and Yoshi is being taken away, simply hit reset. You can now start the game again from the page you died on. Note that this will only work on the US version, as the Japanese game doesn't have a save game feature.
Black Yoshi (2-2)
Go to Bone Dragons Dungeon in Story mode (page 2, board 2.) Go almost all of the way through the level to the tulips. Go to the tulip to the left of Miss Warp #4. Stand in front of the tulip and eat it. Fire yourself upward and break out of the egg near the ceiling. Pop the "?" bubble and grab the Soccer-Ball like egg then falls out. Now complete the rest of the level as you usually would. When you go to the Character Select Screen, you'll be able to select Black Yoshi.
Pop Bubbles Without Eggs
Want to pop a bubble but don't have any eggs? Here's how to do it: Simply keep bumping/jumping on it (beware of pits) and eventually it will pop.
Hidden Mario Paint Tune
Go to the Trial Mode menu in Yoshi's Story and wait. Let the music play through a total of eight times -- when the loudest xylophone-ey sound disappears then reappears, it has played through once. After eight times, the music will stop and be replaced by a tune from Mario Paint, then resume.
White Yoshi (3-2)
Here's how to find the white Yoshi in Page 3-2 (Tall Tower): Proceed to the first leaf and the message block that introduces it. Drop down to find Miss Warp (2) and a message about a big egg. As you climb the platforms back up, drop to the left and pop the "?" bubble. Grab the white egg, and finish the stage.
Black Yoshi (2-1)
To find the black Yoshi in page 2, level 1, find the tulip that turns you into an egg and shoot yourself up. You will land on a platform with a bubble -- pop it and you get the black Yoshi egg. You will be able to select Black Yoshi once you finish the level. Note that you can only have ONE Black Yoshi at the time.
Black Yoshi (2-3)
Another black Yoshi: Go to Page 2-3. Go through the level until you find a Help Box that tells you about a "big egg." From there, go to the left and jump on the last floating rock, then jump on the one above that, and shoot the "?" bubble with an egg. You will receive the black egg. Beat the level and you have the black Yoshi. Note that you can only have one black Yoshi at the time.
Lava Walk Glitch
To do this trick you must be in Level 2-2 : Blargs Pit Play the level until you reach the first heart. Jumps on Blarg's head, get the heart and then try and aim back for Blarg. In doing so you will get hit and lose life, but the petals won't fall off. You will land underneath the lava and be able to walk around down there.
Black Yoshi (2-4)
Go to the #4 Torrential Maze on Page 2. When you start, keep heading upward through several rooms until you get to a room that has ghost vines coming from the ceiling that you can barely see from the ground. Jump from vine to vine, if you're fast enough, you'll come to an edge with a floating bubble. Pop the bubble and grab the large egg that looks like a soccer-ball. Finish the level as usual by collecting fruit. When you turn to the next page, a black yoshi will be with the other six. This Yoshi likes to eat everything, and he gets three hearts for eating any fruit or shy-guy. His eggs also make a larger explosion than the regular ones.
Rotate Pop-Up Pages
To get a better look at the stage select pop-up displays, you can turn them slightly with the C-Buttons and zoom in and out with R and Z.
White Yoshi (3-3)
On Page 3 Area 3 starting from Miss Warp 3 go right. When the road splits with a vase at each end, go in the upper vase. Then go right and enter the upper vase. You should see a dog and a red/orange pipe south of you. Go right and go into the first red/orange pipe to enter a hidden cave. Go right and throw an egg at the bubble. You will now receive a large white egg. Eat the remaining fruit on the level and on the next page and you will be able to choose the White Yoshi.