Life Underflow Glitch

This glitch must be done in the final stage of the game, World 6-8, and you must have 1 life to be able to execute the underflow. Early in the stage, when you have four numbered doors to choose from, enter Door #1.

There, go along the corridor to a ! Switch near a long lava pit. Here, you need to carefully angle your jump so that you will land in the lava and, in turn, leap onto the ! Switch. I find that jumping over the switch, and hugging the wall next to the lava while facing left works best.

Landing on the lava initially will kill Yoshi; however, Yoshi will also leap up from the burn during his death animation. If he strikes the ! Switch in that time, he will be considered to be alive again, although one life has already been lost. Die again by jumping in the lava, and his lives will underflow from 0, and you'll find that Yoshi now has 999 lives!

Contributed by: Anonymous 

Make Eggs yellow and red

It's best to have a full supply of green eggs for this trick. Find a place in a level where you can aim straight up without hitting anything else (ie: level 6-8 would be a good one, after you hit a door, but don't go in yet). Stock up on eggs if you don't have any, then aim straight up. Throw an egg and after it hits the celeing once, have Yoshi catch it with his tongue. It should stop bouncing and be a yellow egg (if it was green to begin with). Throw another egg, this time letting it hit the celeing twice, then catch it. It should have turned red. Doing this trick right will help you make your score better, as red eggs give 2 stars that can be used on the Baby Timer that appears when Mario falls off Yoshi's back.

Contributed by: SuperMarioFan 

Eating Baby Mario

You must have the +10 or +20 star item in your pause screen or it won't work. It works on any level that has a metamorphosis bubble, but it works best on level 5-5 (Goonie Rides!!), where I discovered it. In 5-5, reach the first middle ring, and then you will notice the metamorphosis helicopter bubble ahead. Don't touch it yet. Instead, walk to the edge of the cliff. You will see the white Goonies flying your way. Let one hit you and let baby Mario cry in the air. Now, before the timer runs out, run left until the helicopter bubble is at the right edge of the screen. Don't move from there. Baby Mario will float around the helicopter bubble. Let the timer reach zero. When the red Toadies come and begin carrying him away, lick baby Mario from them, and quickly touch the helicopter bubble while the timer is still 0. When you finish morphing, the Toadies will come back and try to take baby Mario with them, even though you're a helicopter (Don't touch the baby while they are trying to take him, or you will freeze the scroll of the screen!). Now, when all four Toadies are about to take off with baby Mario, immediately pause the game and activate a +10 or +20 stars item. The red Toadies will let go of baby Mario, but he will still be crying in his bubble (and you are a helicopter!). Now touch baby Mario as a helicopter. The bubble will pop and then baby Mario will be stuck in a tiny bubble that doesn't even close around him (If you dont touch him as a helicopter, theres a glitch when the helicopter runs out: youll get Mario back, but the timer wont countdown if you get hit, as long as you dont touch a helicopter bubble again). Now, you can do one of two things:

a) Wait until the helicopter power runs out. If that happens, you will be transformed back into Yoshi. But notice anything strange? Baby Mario is still in that tiny bubble, and he is off your back! Now this is the cool thing though. You can lick baby Mario and he will go into Yoshi's mouth! If you swallow him, he will turn into an egg that can't damage Goonies! If you spit him back out, he will still be in the tiny bubble and slide around until he falls off the stage. You can't even lick him back into your mouth!

b) Head to the Yoshi Block as a helicopter at the end of this part of the stage. Avoid the Goonies and Green Piranas, and hit the Yoshi Block. The baby will transport where you are, and you will transform back into Yoshi. But the funny thing is that once again, you have no Baby Mario on your back. And Mario's bubble will return to normal size, but he will start floating up infinitely! You will lose him unless you can lick him before he floats away. Now, you can swallow him again and turn him into an egg, but if you spit him out, he will float around in his bubble up and down and move horizontally (you'll see what I mean) and won't stop. If you happen to spit him at a winged cloud, he will activate it but Mario will explode in the process! You cannot lick Baby Mario back into your mouth if you spit him out either.

These are fun glitches to try but remember that you must have the +10 or +20 star item and must have a metamorphosis bubble in the course. I have succeeded in other courses with many Yoshi shapes. But let me warn you that if you pull off this glich, you cannot leave the course or beat it without pressing start and select. Oh, and you will have baby Mario on your back again if you do leave the course. Have fun pulling this one off, gamers!

Contributed by: reaverz 

Unlock secret levels and bonus games in each world

To unlock a bonus level and one of the 6 bonus games (when you get a flower on a roullete on the end of the level), finish a world with a 100 on each level to unlock the level and bonus game. These levels are tough for beginners. Here are the bonus games unlocked in each world:

World 1: Flip Cards
World 2: Scratch 'n' Match
World 3: Drawing Lots
World 4: Match Cards
World 5: Roulette
World 6: Slot Machine

Contributed by: peach freak 

Instantly Kill Naval Piranha

When you are in the hallway right before you reach the room of World 3's boss Naval Piranha, start to swim slowly into the room, until you are right in front of the column of falling water. You can just see the untransformed Naval Piranha, but you haven't gone far enough to trigger Kamek's appearance. There, jump straight up, and, before you fall, aim and shoot an egg at the Piranha. When the egg hits the Naval Piranha, Kamek will appear, scream "OH MY!!!" and then flee, and the Piranha will be destroyed, without you having to battle it.

Contributed by: RandyPandy 

Null-Egg Glitch

Note that improper execution of this glitch can and will lead to the game hanging. First, in World 2-2, find a Mouser. Let it grab one of Yoshi's eggs; while the Mouser goes off-screen, take back the egg. At this point, the "egg" is counted as an empty slot, although you have it. Get a Skull-capped Mouser to enter the inventory by making it spawn on-screen, then complete the level as normal. Go to World 1-8 and proceed as normal to boss: before entering the boss door, have only one egg available. Attack Salvo on the other side of the door by using this egg and the smaller bodies that split off of Salvo when hit -- do not destroy any of them by jumping or ground-pounding them. After, go to any level: the "door unlock" cutscene from the end of World #-8 levels will immediately play. Play through the glitched level without falling into lava or being eaten by Piranha Plants, and do not lose the Key. In this manner, you will cause the game to consider that the credits have rolled, as if you've finished the game. You can also experiment with this glitch to get certain other items in your inventory, such as a glitch pipe to World 1-1 that allows quick level completion.

Contributed by: Anonymous 

World 1-1 Warping: Skip World 2-1

In World 2-1, partway through the level you need to go down a pipe with a red down-pointing arrow on it (you will see another similar pipe to the right of there, with an up arrow). Whilst standing on it, press Down and the Jump Button together. You will glitch the game and warp to the top-left bit of World 1-1. Flutter Jump to the right as much as possible whilst falling (you'll die if you don't) and you'll fall on part of World 1-1. You can finish the level from there as you would 1-1, with the benefits of being able to gain extra Red Coins, Stars, and Flowers from the level; further, the score earned will be counted towards 2-1 and it will also count as you finishing 2-1!

Contributed by: Anonymous 

World 1-1 Warping: Skip World 1-4

In World 1-4, partway through there is a locked door next to a pipe. Enter the pipe. When you land, begin holding the button to aim an Egg, then walk backwards and hit the Hothead so that you're hurt. Go on the platform to the right without grabbing Baby Mario, then Flutter upwards towards the exit. Yuo should end up grabbing Mario while above the screen. You will glitch the game and warp to the top-left bit of World 1-1. Flutter Jump to the right as much as possible whilst falling (you'll die if you don't) and you'll fall on part of World 1-1. You can finish the level from there as you would 1-1, with the benefits of being able to gain extra Red Coins, Stars, and Flowers from the level; further, the score earned will be counted towards 1-4 and it will also count as you finishing 1-4!

Contributed by: Anonymous 

World 1-1 Warping: Skip World 3-1

In World 3-1, partway through, you'll reach a Middle-Ring. Nearby, you'll find a watermelon-seed-spitting monkey. Jump from his head to up and above the Middle-Ring; you'll get an extended jump boost. While doing floating above and to the right of the ring, you'll want to try to enter the hidden bonus area. You will glitch the game and warp to the top-left bit of World 1-1. Flutter Jump to the right as much as possible whilst falling (you'll die if you don't) and you'll fall on part of World 1-1. You can finish the level from there as you would 1-1, with the benefits of being able to gain extra Red Coins, Stars, and Flowers from the level; further, the score earned will be counted towards 3-1 and it will also count as you finishing 3-1!

Contributed by: Anonymous 

World 1-1 Warping: Skip World 4-7

Partway through 4-7, you will be able to shoot down a springball that's hidden above the screen. (It is where the fish enemies fly leftward at you and there's an impassable wall to the left.) Shoot down the springball and use it to reach another. As you use this one and go to the next screen from the jump, hold Left. You will glitch the game and warp to the top-left bit of World 1-1. Flutter Jump to the right as much as possible whilst falling (you'll die if you don't) and you'll fall on part of World 1-1. You can finish the level from there as you would 1-1, with the benefits of being able to gain extra Red Coins, Stars, and Flowers from the level; further, the score earned will be counted towards 4-7 and it will also count as you finishing 4-7!

Contributed by: Anonymous 

Carry Big Eggs to Other Levels

When getting a Big Egg (as in World 2-7), you can carry it to another level. Go to the Goal Ring and past it to the right side of the screen. Aim the Big Egg straight up, launch it, then lick it with your tongue; repeat as necessary until the Big Egg is launched to to the right and about half off-screen. Then enter the Goal Ring. The next Yoshi to come will pick up the Egg, carrying it with the others and Mario to the next level. Note that the Big Egg's graphics will glitch up, but it'll retain its normal functions.

Contributed by: Anonymous 

Coin-Based Level Warping

Note that this glitch requires a controller that allows pressing both Left and Right on the D-Pad simultaneously.

Begin by collecting a certain number of coins and returning to the level selection screen. The amount varies upon the level you wish to warp to. 68 for example will bring you to the final level, but depending on the amount you can go to any level, including glitch levels. With this achieved, use Start and then Select to leave the level and return to the map. There, press Left and Right together, then an less than half a second after begin holding the A Button. The cursor will glitch up a little, but you will soon transition to the named destination level.

Note that this glitch can affect level progression significantly and make it so certain levels are only accessible with further use of the glitch. Results can be variable and may require several tries for the desired result.

Contributed by: Anonymous 

Duplicate Red Coins

In several levels in the game, there are Shy Guys which are flying in the air with a red sack beneath them. Normally, if you eat or kill the Shy Guy, it will drop the Red Coin. If it drops the Red Coin, but you don't pick it up and instead run off-screen, you can then return to where the Shy Guy appeared. The Red Coin will be there still, but that Shy Guy will come in holding yet another Red Coin.

Contributed by: Anonymous 

Extra 1 - Disable Auto-Scrolling

During the World 1 Extra level, you can disable the autoscrolling in the level. To do this, you need to bounce repeatedly on the bat enemies that appear at the start of the level in sequence, doing so until Yoshi is eventually off-screen. Then Flutter Jump to the right and past the first stony wall that appears from the ceiling. Once past, you can still play the level with Poochy, but without the autoscrolling that would otherwise painfully limit your abilities and overcomplicate things.

Contributed by: Anonymous 

World 3-4 Boss Tips

At the end of World 3-4, you'll encounter a boss in which you fight in the foe's stomach. If you do not move left/right at all on entering the stomach, you will never be hit by the acid. Furthermore, try to angle your egg shots to hit the sides of the uvula at the top of the screen: for reasons unknown, hitting the target from the side, as opposed to just aiming straight up at it, does significantly more damage!

Contributed by: Anonymous 

Hidden Stars During Final Boss

During the final boss fight against King Baby Bowser, it is possible to get hidden stars that count toward the baby timer. In the second phase of the fight, hold up on the D-Pad before firing one of the big eggs. Instead of firing them in the background at Baby Bowser, you will shoot the egg upwards at enemies off screen and a star will drop from the sky. You can do this continuously to build up your baby timer, allowing you to more easily finish the level with 30 stars if you get hit during the final boss.

Contributed by: _Blur_ 

Title Screen Stars

To append stars next to the logo at the game's title screen, you must get 100 points in the secret Extra Stage in a given world. The Extra Stage in itself is unlocked by getting 100 points on the other eight levels in the world. One star will appear for each Extra Stage completed in such a manner, for a total of up to six stars at the title screen.

Contributed by: Master_of_Majora, Anonymous 

Codes

Contributed by: ned_nelson 

Get 6 NEW Secret Levels

Beat the game to get a whole new set of 6 levels not found in the original Yoshi's Island.

Contributed by: ReyVGM 

Extra 1 - Disable Auto-Scrolling

During the World 1 Extra level, you can disable the autoscrolling in the level. To do this, you need to bounce repeatedly on the bat enemies that appear at the start of the level in sequence, doing so until Yoshi is eventually off-screen. Then Flutter Jump to the right and past the first stony wall that appears from the ceiling. Once past, you can still play the level with Poochy, but without the autoscrolling that would otherwise painfully limit your abilities and overcomplicate things.

Contributed by: Eevee-Trainer 

Special Ending

Obtain 100% in every level - the main eight of each world, plus extra and secret levels. You'll get a special message (which seems to indicate how many lives you lost accomplishing this feat) and an ending sequence to accompany it!

Contributed by: Eevee-Trainer 

World 3-4 Boss Tips

At the end of World 3-4, you'll encounter a boss in which you fight in the foe's stomach. If you do not move left/right at all on entering the stomach, you will never be hit by the acid. Furthermore, try to angle your egg shots to hit the sides of the uvula at the top of the screen: for reasons unknown, hitting the target from the side, as opposed to just aiming straight up at it, does significantly more damage!

Contributed by: Eevee-Trainer 

Life Underflow Glitch

This glitch must be done in the final stage of the game, World 6-8, and you must have 1 life to be able to execute the underflow. Early in the stage, when you have four numbered doors to choose from, enter Door #1.

There, go along the corridor to a ! Switch near a long lava pit. Here, you need to carefully angle your jump so that you will land in the lava and, in turn, leap onto the ! Switch. I find that jumping over the switch, and hugging the wall next to the lava while facing left works best.

Landing on the lava initially will kill Yoshi; however, Yoshi will also leap up from the burn during his death animation. If he strikes the ! Switch in that time, he will be considered to be alive again, although one life has already been lost. Die again by jumping in the lava, and his lives will underflow from 0, and you'll find that Yoshi now has 999 lives!

Contributed by: Eevee-Trainer 

Title Screen Stars

To append stars next to the logo at the game's title screen, you must complete every single level in a given world: this includes the extra levels earned by getting 100 points on the other eight levels in the world. One star will appear for each world completed in such a manner, for a total of up to six stars at the title screen.

Contributed by: KeyBlade999 

Alternate Title Screen

Simply beat the game 100% and the next time you boot up yoshi's island the game's title screen will show yoshi's island but it will be night instead of day

Contributed by: Meatwad3000 

Touch Fuzzy Get Dizzy: Unlimited Lives

Grab a Melon Bug (the creature that rolls up into a ball) and go to the pipe with Shy Guys jumping out of it. Spit the Melon Bug close to the pipe on the left-hand side. When Shy Guys jump out, after a while you will get a "1-Up" for each time a Shy Guy hits the Melon Bug when it is in its melon form.

Contributed by: Y2JosHBK386 

Get hundreds of extra lives on level 4 – 1

After you have gone over all the hills there is a pipe that ‘Shy Guys’ come out of. Ignore them and go past the pipe and get rid of the Killer Plants in the next two pipes to the right (one above and on the ground). A Kooper is walking between the two pipes on the ground. Jump on the Kooper and send his shell spinning between the two pipes. ‘Shy Guys’ continue to jump out of the pipe on the left and every time the Kooper shell hits them you will hear a different sound that means you’re getting lives! Stand on the pipe on the right and the lives will continue for as long as you stay on this screen.

Contributed by: borris_m 

Naval Pirhanna Boss Instant Win

When entering the arena, do not pass the end of the stone colonade that is at the very edge of the large arena room. This will allow you to see the small pirhanna plant without activating the boss battle.

From here, you can fire an egg at the pirhanna plant and destroy it with one hit. This forces Kamek to appear and say 'OH MY', before fleeing. Having already destroyed the plant and scared Kamek, you will not have to fight the Naval Pirhanna, thus avoiding a potentially difficult boss battle.

Contributed by: Inquisitorphil 

Lucky 7's

In any World, whenever you get your World Score to 777, you will earn 7 lives.

Contributed by: peach freak 

Earn Point Stars (Mario Bros.)

Contributed by: Nightmare Squad 

World Score Bonuses and Prizes

Collect a certain amount of points in a world to get a special surprise. (Note: the first three apply for all 6 Worlds.)

Contributed by: Nintendo fan 302 

Codes

Contributed by: tombomb2003