This post is no longer up to date. I'll remove this message when it is. But keep in mind that levels now retain the version that they were made in so in most cases, a glitch that is patched will still work in levels that were made before the patch.
- Flying Cannons [Works as of v. 1.3]: Attach cannons to the undersides of conveyor belts in such a way that the one cannon falls onto another in mid-air. The cannons will stick together and continue moving through the air in the direction that the conveyor belts were carrying them. If a spring is used to launch a cannon during this, the cannons will freeze in mid-air after being launched. (Found by Luigisopa)
- Track Momentum Conservation (Launching objects off tracks vertically faster than normal) [Works as of v. 1.3 (But with physics changes when launching to the side. Momentum can no longer be maintained, at least with blue skulls... I think?)]: Objects moving on tracks seem to have a bit more speed when moving diagonally upward. This speed can be conserved if the object leaves the track and reconnects with another track in just the right way. By using multiple diagonal tracks above each other, the effect can be stacked in order to shoot objects, blocks, and enemies upward at a very high speed. (Additional juicy details) (Found by Phantal)
- Super Spring Jump [Fixed in v. 1.20]: In a Super Mario World level, hold an object and jump on a spring while mashing left and right quickly. If done correctly, you'll jump way higher than normal. (Found by Sockfolder and zilchfox)
- Spring and Note Block Clipping: By placing a bunch of note blocks and/or springs next to each other and against a ceiling or other object in certain ways, it is possible to cause Mario or an enemy to clip through various barriers.
- Bill Blaster + Note Block Zip aka "Phaseporting" [Works as of v. 1.3]: (Video) Place a Bullet Bill Blaster on a note block one tile above the ground so that it bounces and place another Bill Blaster adjacent to it. Position Mario under the note block so that he is pushed slightly into the other Bill Blaster whenever the bouncing one pushes down on the note block. Jump when the bouncing blaster is at its lowest point, and Mario will zip up between the two blasters and end up on top of the non-bouncing one. (Found by DJNfinity)
- Constantly falling Bowser [Fixed in v. 1.3]: If you put Bowser on top of a skull platform and place a ceiling two blocks above the skulls, he will become stuck in his falling/jumping animation whenever he tries to jump and will be unable to act except for moving his head. While in this state, Bowser is able to ride shells launched from a cannon. (Found by ExplosiveSheep)
- Donut Thwomp Push [Fixed in v. 1.20 for thwomps only]: A thwomp with space below it will be pushed up a little bit when a falling donut block passes through from above. If repeated enough times, the thwomp can be pushed upward through one-way platforms. If used to push the thwomp through solid blocks, it will move only a few pixels and then stop. Nonexistinghero notes that the same effect can be achieved with wall-mounted cannons (still works in v. 1.3).
- Conveyor Mole Projectile Glitch [Fixed in v. 1.3 for any future levels]: Place a mole on a conveyor belt and then stack a large projectile throwing enemy (Bowser or fat Hammer Bro) on top of it. Over time, the enemy's projectile speed will increase to insane speeds. If you wait long enough, Bowser will clip through the wall. The same effect can be achieved without the conveyor belt if using a big Bowser. Also, after around 25 seconds, there is a chance that Bowser will die upon pressing a P-switch (or when the effect wears off) if the wall he is pressed against is blocks (as opposed to a one-way wall).
- Wall jumping in SMB1, 3, and World [Works as of v. 1.21]: Run and jump off of a moving platform (skulls) while ducking, then with perfect timing and positioning, jump upon hitting a vertical wall. If done correctly, you'll be able to jump.
- Light Speed Mario (Bounce momentum stacking) [Works as of v. 1.3]:
- Sticky Fly [Works as of v. 1.21]: In a Super Mario World themed level, fly with the cape up into a long row of invisible blocks and hold left. If done correctly, you'll slide along the row and activate all of the invisible blocks without dropping back down.
General Gameplay Glitches
- Phantom Munchers [Works as of v. 1.3]: If a muncher is hit in mid-air by a sideways spring, it can be put into a strange "phantom" state upon landing. In this state, Mario and enemies will be able to pass through the muncher, although Mario will still take damage, and it'll have some other interesting properties as well. (Found by /u/Mariomaster2015 and /u/Luigi86101)
- Clown Car + One-Way Block Ceiling Clip [Works as of v. 1.3]: By positioning a clown car on a one-way wall, you can jump slightly from the wall-side and stand on top of one of the one-way wall objects. Once in this position, it's possible to jump upward and clip into a ceiling above.
- SMB1 Vine Clip [Fixed in v. 1.3]: In any Super Mario Bros. themed level, place vines hanging from a solid ceiling and one or more blocks against a corner as shown in the video below. Then, climb up the vine next to the corner block and press toward the block once you are at the ceiling. If done correctly and with a compatible block, you will pop up into the ceiling above the corner block. You can run around at that level or jump to move up a tile further into the ceiling. (Submitted by god_of_masks)
- Door Glitch (Invincibility) [Fixed]: This glitch can be activated by going through a door located on spikes, just as you are about to lose your invincibility from losing any power-up higher than "Super" Mario (i.e. a flower, raccoon tail, propeller suit). Upon passing through the door, you will be invincible for the rest of the level. (Alternate method [Fixed in v. 1.20]: Slide as big Mario under a muncher overlapping with a door and enter the door without getting hit.)
- Wrong State POW Glitch [Works as of v. 1.3]: By catching a POW block that after it has fallen off a track, but before it has hit the ground, the POW block will remain in the falling state for a moment after you drop it, allowing it to pass through semi-solid platforms (clouds or other one-way platforms). (Found by MYCRAFTisbest)
- Yoshi Eating Blocks [Maybe fixed in v. 1.20?]: In the Super Mario World style, Yoshi can eat a solid block placed above a coin or sometimes duplicate the coin. It is possible to eat rotating blocks, question blocks, hidden blocks, hard blocks, clouds, ice, donut blocks, note blocks, and music blocks. (Found by stendec365 and others)
- Frozen Yoshi Glitch [Works as of v. 1.21]: While underwater, eat a cheep cheep with Yoshi, but take damage from spikes before the cheep cheep reaches Yoshi's mouth. With the right timing, Yoshi's body (apart from his legs and eyes) will be frozen, unable to turn around, and unable to spit out the cheep cheep or eat anything else. This can be done in New Super Mario Bros. or Super Mario World themes. (Found by luigisghost227)
- SMW Yoshi/Shell/Flower Crash: In a Super Mario World themed level, carry a shell as small Mario and jump between a Yoshi and fire flower which are next to each other. At the precise moment that you hit both, be turning in midair so that Mario is hidden by the shell. If all goes well (?) you'll crash the game. (Video, Video 2)
- 1.5 Height Mario [Fixed in v. 1.3]:
|Via DOMOHEAD of Reddit|
- Rail-Glitching Blocks (Putting two blocks on the same tile) [Fixed in v 1.20 - Levels made using this glitch will be played as if only one block is in a tile and the glitch can no longer be performed]: This is the glitch that is used to make invisible platforms, fake platforms (which you fall through), and any other "weird block glitch" which combines the attributes of two blocks into one. Working with this glitch is complex, so I recommend checking out the guide on /r/MarioMaker for all the helpful details. I wouldn't be able to write it better than they already have. In general though, put a block on a track, drag the track on top of another block, then use the track tool to remove the track, leaving both blocks on the same tile. To see the basics of how to do it in the editor, check out this video by GameXplain. Mysterio64 has also made a reference chart to help you understand the results of each block combination.
- Out of Bounds Underwater Softlock [Fixed in v. 1.3]: If you have an area or sub-area which is underwater and have no objects placed above the lower half, you can place a warp pipe one tile below the thick dividing line in the editor so that when Mario comes out of the pipe he will be going upward. Upon trying to get out of the pipe, Mario will be above the playable area and the timer will not resume, nor will you regain control of Mario, forcing you to reset the game. (Found by NOKAUBURE)
- Intangible Wall Glitch [Fixed in v. 1.20]: Before creating a sub area, adjust the length of your level so that you add one tile per "screen" of length. This is easiest if your level is only one screen long since you only need to move the flag one tile and don't need to measure screens. Then, drag Mario into a pipe to create a sub area. Without adjusting the sub-area's size, you'll find that the final column of tiles will be glitched. Enemies and pipes cannot be placed in it and blocks that are drawn in it will not be solid when the level is played. (Found by metalflygon08, detailed and submitted by Chris Fritz)
- While collecting a powerup, you can pass upward through invisible blocks without activating them. [Fixed in v. 1.20?] (Found by Luigisopa)
- Cannon sliding [Works as of v. 1.3]: Cannons placed on walls can be pushed up a little bit at a time by throwing objects up at them (easiest in Super Mario World style) or by using trampolines. It will keep going until it stops at a ceiling or, if there is no ceiling, it detaches and falls down. (Found by genotaru) Cannons can also be pushed up when a falling donut block passes through them from above.
- Centering a large enemy on a tile [Works as of v. 1.3]: By stacking a 2x2-tile-sized enemy or other large enemy on top of a smaller enemy like a Goomba, the larger enemy will be centered over a single tile. The Goomba can then be replaced with a Podoboo (which can't be stacked on) and then the Podoboo deleted, leaving your large enemy centered in a way that it couldn't be otherwise. (Found by jonahhl)
- Checkpoint clip [Works as of v. 1.3]: Place a checkpoint flag so that the lower half is inside a block, but with a space below that. After triggering the checkpoint and dying, you'll respawn in the area below the flag. (Video by GameXplain) (Found by Waverunner56)
If you know of any additional glitches that aren't on this list, let me know and I'll add them!