List of Super Mario World glitches
In order to do this glitch, the player must go to Yoshi's House and keep pressing the and buttons. Sometimes the birds and berries will pause and the smoke from the fireplace will skip. If the player's lucky, the smoke will be glitchy. If the player can't reproduce the glitch after about a minute, they must re-enter Yoshi's House and try again.
To do this very minor glitch, all the player has to do is duck and jump on a fence. As long as Mario or Luigi doesn't touch the ground, he'll be ducking each time he jumps off the fence.
To make this glitch, the player must have already pressed the Red and Green ! Switches. The player must have Cape Mario and a Yoshi in Star World 4. At the level's secret exit, they must make Yoshi keep the Key in his mouth and fly with Cape Mario to hit all green ! Blocks at the left. If the player drops the Key, it will be an item that changes from a Yellow Beach Koopa and an upside-down Cheep-Cheep.
Glitchy Graphics from Defeated Enemies
The balls on Iggy's and Larry's platforms can be destroyed by the sliding attack, as can the Grinders (using a triangle block). This results in glitchy graphics, most likely because the developers did not intend for these enemies to be defeated. The same thing happens if Mario does a nose dive while a Big Steely is present; the Big Steely is defeated, though its sprite appears as Princess Toadstool's head colored red.
In order to do this glitch, the player must go to the end of Chocolate Island 3. Under the goal, the player must jump off Yoshi to the Giant Gate so that the screen does not scroll up. If done correctly, Mario is barely seen when he finishes the level, and because Mario is not present on the bottom of the screen, the screen begins to flicker in many colors as the stage begins to fade out. When he comes back to the overworld map, the entire world is glitchy and colored with red and blue. If Mario visits Forest of Illusion or Valley of Bowser and comes back to the main overworld, the entire world will be ivory colored instead. The glitch ends if the player completes a level or visits Star Road.
In Donut Secret 1, Mario must enter the Warp Pipe to the secret underground area. While Mario is on the ground, the pipes are orange, however, when Mario flies up and comes down, both pipes are miscolored green. Sometimes, the pipe gets only one half green-colored.
The player can do it in Donut Secret 2. To do this, the player must have a blue Yoshi. Eat the Yellow Koopa Troopa next to the 4 spiked enemies. Fly to the left of the pipe near the exit and if the player did it right, the wings will disappear and when the player spits it in the pipe, then it will turn into something glitched.
Green Berries and Music Speed
Music speed increases when the Timer reaches 100, warning the player of the time limitation. Usually this can only happen once in a given level. However, on Funky, where the green berries appear, the player is given 20 extra seconds for each berry eaten by Yoshi. If timed correctly, the player can eat all 9 green berries, each when the Timer is somewhere between 81 and 99 seconds, and it increases the music speed up to 10 times, making it very fast. If an extra 11th green berry is eaten, the music will slow down drastically.
The glitch was fixed in the Super Mario Advance 2 remake, as the music does not speed up should the player attempt to try this glitch.
Spin Jump Sound Glitch
In #4 Ludwig's Castle, in the room with the spiked ceiling falling down, the player must wait for it to touch the ground. If the player Spin Jumps afterward, the sound played is the one that plays when the ceiling hits the floor, instead of the normal Spin Jump sound.
The player must find a Fire Flower and Feather in purse (or vice versa), Yoshi and level with berries, like Yoshi's House. By collecting the stored item while eating a berry with Yoshi at the same time, the game freezes, as well as causing Mario to flash from red to green like if he touched a Starman. It can also have a more helpful effect of infinitely raising the player's coins, giving the player up to 99 lives in the process. The only way to end the glitch is by exiting the level by pressing Start then Select. (if a level is completed)
This is a glitch in Vanilla Dome 2. Mario must be Super, Cape, or Fire Mario. The P-Switch must be active; when the player sees a rectangle-shaped structure of coins sitting on the ground, Mario/Luigi must duck while running, and wait for the P-Switch to become inactive. After that, he must stop ducking. He will be in the floor. Even more worth noting, Yoshi and any grabable items will slide and will not react to gravity. This glitch is not possible in the GBA remake.
Falling Through the Floor
In Vanilla Dome 2, it's possible to fall through the floor via a glitch in both the original game and the Game Boy Advance remake. Towards the end, the player has to take a left and go through the "secret" passage. Then the player has to get a Buzzy Beetle shell and toss it at the first two blocks. Then the player has to quickly get a running start and slide under the blocks before they harden. Once there, the player must not release the button. Once the player is completely surrounded, if the player presses , Mario will Spin Jump through the floor, leading to his demise.
In the Pipe
This glitch occurs in both the original game and the GBA port. In any level with a pipe that extends and retracts into the ground, the player must get an item that Mario can carry around (Koopa Shells, P-Switches, etc.) and drop it on the pipe. When the pipe retracts, the item falls normally, however, when the pipe extends, the item gets stuck in the pipe. The item "vibrates" back and forth and eventually move out of the pipe after a few seconds. Yoshi can also be in the pipe, as long as Mario isn't riding him.
In either the SNES or GBA versions of the game, in a level with a P-Switch or a key, the player can dash to the direction of a wall holding a P-Switch/key. To do the glitch, Mario must throw the P-Switch/key and swiftly dash to the wall. Mario gets stuck between the wall and the P-Switch/key and starts to shake. The player can get Mario out of there by jumping or grabbing the P-Switch/key.
Walk Through the Floor
In some of the underground levels, it's possible to walk through the floor to the exit. First the player must grab a Koopa Shell or flipped Buzzy Beetle, then move between platforms that can defeat Mario almost closed in. The player must jump on it and Mario is able to walk through the ground until they reach an area requiring a jump.
The player must go to Donut Secret 1 and access its bonus area. The player must get the P-Balloon and hold left and right on the directional pad. Mario travels very swiftly, and if the player holds left and right with the P-Balloon and touches a wall on the side of the screen, Mario loses a life.
Wall Death 2
Yoshi and Pipe Glitch
The player must place a Yoshi on an extending and retracting pipe. Whenever the pipe moves, Yoshi moves blocky. This glitch occurs in both the original SNES game and the GBA port.
If the player has Yoshi grab a berry on his tongue while it is extending, and then the tongue later attaches to an enemy in the same motion, the berry will be left where the enemy was, without being swallowed. The berry will also lack animation, but can still be eaten. In some cases, the berry will actually change color (and behavior). For example, on Funky, the first green berry (after being moved) will sometimes turn into a red berry if Yoshi eats the nearby Jumping Piranha Plant or another berry.
One Yoshi, Two Yoshis, Invisible Yoshis
In the level Chocolate Island 5, if Mario/Luigi grabs the two P-Switches (how to do it can be read here) and bash the Yoshi block with it, the block will create two Yoshis, but only one appears. When the Yoshi falls into an abyss, the other one appears. If the player falls into an abyss and waits until Mario and Yoshi disappear while jumping, he is riding on an invisible Yoshi.
By throwing an enemy or object at a block very close to it, the block can be duplicated near it, unveiling the item, leaving the original block untouched. This can be done to either side of the block, above it, or above-diagonally to either side.
Also the game differentiates certain items by the block's horizontal position in the level. For example, blue P-Switches and gray P-Switches are actually the same object, but their type depends from the horizontal position of the blocks that contain them. Thus, by duplicating a block to the side with a P-Switch inside, it will give a P-Switch of the other color.
End the game with Yoshi
This glitch happens in Yoshi's Island 3. The player must go with Yoshi into the Yellow Warp Pipe. Once they are there, the player must press the P-Switch and Yoshi must eat the pressed button and spit it out. It causes a Cheep-Cheep to appear and the player must do the same nine more times. Doing this, Mario must leave Yoshi on the line of blocks and leave the area holding the secret button. The player must to find Yoshi, press the P-Switch, eat and spit, then let him fall and ride an invisible Yoshi near the edge. The invisible object in his mouth must be spat, and Mario becomes Cape Mario. In the area near the Koopa Troopa, the player must make Yoshi to eat the shell in the same time Mario becomes Fire Mario. They must, then, drop Yoshi and throw a fireball, and ride Yoshi again. Drop the Cape Feather and use it. After this, the game's end screen appears, but the level music still plays. 
Everlasting Cloud Ride
The player must shoot a fireball at a Lakitu who is riding in a cloud, and then make sure to collect the coin. The player must then jump in his cloud and it will last forever.
Everlasting Grab Blocks
This glich occurs in both the SNES and the GBA versions of the game. If the player takes a Grab Block and go through any pipe, it will never disappear. The player can take any carryable enemy (like Galoombas) through a pipe and it will never jump on Mario, and a Bob-omb will never explode. If done with a Buzzy Beetle shell, it will be colored gray, not blue.
Grabbing Two Objects
If two things (like P-Switches, Shells (two shells doesn't work), Springs, etc.) are placed in the same place and Mario/Luigi runs (pressing without dropping), he will catch the two things, then crouch and slide to grab the objects (the cause of dropping not button), the player will take the two things at the same time. A side effect of this occurs if the player stops holding Y and if Mario is small, killing him between the two items (though this must happen with the two items being identical, like two keys).
In the Pillar
This requires precise timing. If Mario or Luigi spin jumps at just the right time while a pillar is falling in a castle, he'll be inside the pillar.
Item Stock Glitch
In Yoshi's Island 1, the player must have Yoshi and Fire power. On the part with the Jumping Piranha Plant and a Rex nearby, Yoshi must stick out his tongue, Mario or Luigi must shoot the Rex with a fireball, Yoshi must eat the coin produced, and Mario/Luigi must collect the coin. Since nothing will be in his mouth, the game will place the nearby Chargin' Chuck in Yoshi's mouth. Chargin' Chucks aren't supposed to be eaten, so the game won't know what to do with it. It will place a glitchy item in the player's Item Stock. Depending on the level, it can show up as many things when used, including a ? Ball, a green Bony Beetle, a green Cheep Cheep, or a glitchy sprite not resembling anything. Regardless, it will act like a ? Ball. This is a way to beat a level with less challenge, but is also considered cheating. Most of the time, due to programming quirks, the game may crash. This glitch was fixed in all remakes and in the Virtual Console version.
Item After the Giant Gate
This glitch occurs in both the original and GBA port of the game. Mario or Luigi must go to a level with a Super Mushroom in the ? Block until the Giant Gate. The player must drop the item and wait it to go through the gate, and, after it is in the other side, finish the level. If Mario walks before the screen changes, he collects the Power-Up.
The player must take a grey P-Switch and go into the pipe. Though the P-Switch has still its grey coloration, it acts like a blue P-Switch.
Renewing a P-Switch
To get this glitch to work correctly, the player must be riding Yoshi. Yoshi must press the P-Switch and eat it before it disappears. When Yoshi spits it out, the P-Switch will be back to normal and the player is able to press it again.
Shell Through the Floor
This is a very simple glitch that is easy to do in various levels of Vanilla Dome. If Mario or Luigi throws a Koopa Troopa or Buzzy Beetle shell while on a very steep slope and faces the slope, it is not be able to climb it, so it goes right through it.
Stomp After Death
If Mario or Luigi loses a life above a Wiggler, he will stomp it, and even gain points, on his way off-screen.
Survive the Fate
It is possible to avoid the death imposed by the timer if the player drops a Fire Flower while on a Yoshi and being with a cape, and eats the Fire Flower at the same time the timer counts 0, letting thus the player survive the death.
The player must bring Cape Mario to an area with at least two Wigglers (three is better); the best place is Forest of Illusion 1, and jump on the yellow Wigglers to make them angry, and float back and forth so that the angry Wigglers are calm again. The player needs to keep jumping on the Wigglers, and the player will gain points as usual. After the player gets 8,000 points, they will get a 1-Up, 2-Up, and then a 3-Up. On the next bounce, the game will display strange symbols that represent five extra lives. More glitchy graphics will appear and they will give large amounts of points in addition to numerous coins.
This glitch was fixed in the Game Boy Advance version.
Ludwig/Roy/Morton Jr. Cheat
This glitch occurs in both the SNES and GBA versions of the game. As a result of this glitch, rather than defeating Ludwig Von Koopa, Roy Koopa or Morton Koopa Jr. with three jumps or twelve fireballs, they can be defeated with a single jump and eleven fireballs, or, more notably, hit with two fireballs and jumped on once.