Super Mario Bros.
Bugs/glitches

Double jump
After grabbing a Mushroom in mid-air, Mario can pull off another jump with the right timing. First, time a jump so that small Mario is on his way down when he grabs a Mushroom. While Mario is transforming, hold A, and he'll jump again when his transformation into Super Mario is complete.

This trick will also work if small or Super Mario drops or jumps onto a Fire Flower.

Fixed in Super Mario Bros. DX?: Yes.
Fixed in Super Mario All-Stars?: No.
NESticle movie?: Yes.

Starman kills fanfare
Grab the flagpole while invincible with Starman power, and the overworld theme will interrupt the "course clear fanfare" and continue to play until the game moves to the next level. (The ideal level for this is World 1-1. Hit the block with the Starman in it, but don't grab it right away. Have the Starman follow Mario up to the first small staircase, then grab it and head through the rest of the level as fast as possible.)

Fixed in Super Mario Bros. DX?: Yes.
Fixed in Super Mario All-Stars?: Yes.
NESticle movie?: Yes.

World 4-2 wacky warp to Worlds 6/7/8 without the Vine
This one will take a while to explain, but basically we'll be using a variation of the "walk through walls" glitch (see below) to get Mario on the right side of the screen when he passes through the area with the Vine that leads to the Worlds 6/7/8 Warp Zone. This will fake out a nearby pipe, which will take Mario to the warp zone instead of the vine! Here's how it's done...

At the beginning of World 4-2, there is a very bricky area with a group of three Goombas near the end of it. Before the Goombas, you'll come across a small hole in the brick floor. Make sure to drop down and get a Mushroom from the last block in the overhang if you're small -- Mario must be "Super" for this glitch. Then, standing above the hole, jump straight up twice so Mario breaks two Bricks [1].

Next, slowly walk to the right (watch out for the Goombas) until the two-block column you just created has scrolled about half-way off the left side of the screen [2]. Go all the way back to the left side of the screen, then duck and jump once. Mario's feet should automatically "catch" the wall, and he will appear to be stuck [3]. (If Mario's feet don't catch the wall, you haven't scrolled far enough. If Mario breaks a block to the right, you've scrolled too far; just break another one above it and try scrolling again.) Release the Down button, and press the Right button once if you weren't already facing right. Now Mario should be sliding through the brick wall -- do not walk or jump until Mario stops at the right side of the screen. When Mario has stopped [4], jump straight up and to the right until Mario is on top of the bricks.

Now, Mario should be on top of the bricks and all the way to the right of the screen. (Important note: Walking back to the left will move Mario away from the right side of the screen, which may cause the glitch to fail. Try to move forward only.) Staying at the right side of the screen, head to the other side of the pit where the three pipes are. Go down the third pipe [5], and voilà -- Warp Zone! [6] (This is the trickiest part because you can't really see what's in front of you because you're at the right side of the screen. If you need to, you can go back a few steps before continuing on, which will give you a little more room in front of you. Be careful not to scroll too far back.)
--[Sent in by WhooHooDoh]

Fixed in Super Mario Bros. DX?: Yes, because of SMBDX's auto scroll feature.
Fixed in Super Mario All-Stars?: No.
NESticle movie?: Yes.

Walk through walls
In 1-4, pass the first firebar thing and stop on the next platform. You'll notice that the ceiling drops down and almost forms a wall. Slowly go to the right until there's about half a block length between the left edge of the screen and that wall. Direct Mario to the left side of the screen, and jump. Mario should hit his head on the ceiling and land on the wall. (If Mario can't fit, you've scrolled too far. If Mario doesn't get stuck, you haven't scrolled far enough.) Now, hold Left and jump rapidly until Mario starts moving backwards through the wall. At this point, you'll be able to walk through to the end of that low ceiling (beware the firebars...). It is possible to repeat this trick anywhere you find similar floor/ceiling/wall combinations.

Fixed in Super Mario Bros. DX?: Almost. After you're stuck you have to duck and jump to get into the wall.
Fixed in Super Mario All-Stars?: No.
NESticle movie?: Yes.

Koopa Troopa factory  [Screen shots: 1, 2, 3, 4, 5]
This might work in all similar situations, but an easy place to do this is World 1-1. Near the beginning of the level, there will be two Goombas walking down from a high platform, onto another platform with a Question Block in the middle. Scroll the lower platform almost all the way to the left end of the screen. With perfect timing you can run back and knock the left-most block from below as the last Goomba walks over it. For some reason, this turns the Goomba into an upside-down green Koopa shell as he dies! If you knocked the Mushroom out of the Question Block as you ran by the first time, the shell will be red.
Another good place to pull this off is World 6-1, in the area where you can find the warp-only 1-Up Mushroom (see screen shots 3 - 5 above). If you're in the right spot, you can consistently turn Spinys into Koopa shells. Since Spinys survive knocks from below, the Koopa shells will also survive, and turn into live Koopa Troopas on the ground...

Fixed in Super Mario Bros. DX?: Yes.
Fixed in Super Mario All-Stars?: No.
NESticle movie?: Yes.

Mushroom magic  [Screen shots: 1, 2]
In World 1-1, at the same part as described above, sprout the Mushroom, then get on top of the high platform. As the Mushroom falls in the pit, try to jump so that Mario goes off the top of the screen as the Mushroom goes off the bottom of the screen. If Mario and the Mushroom are lined up perfectly, Mario will collect the Mushroom off-screen.

Fixed in Super Mario Bros. DX?: Don't know.
Fixed in Super Mario All-Stars?: Don't know.
NESticle movie?: Yes.

Inside the enemy  [screen shot]
As Super or Fiery Mario, run into an enemy. While you're blinking with post-damage-invincibility, get right up inside the enemy, and try to mimic his movements. When the invincibility wears off, you'll be inside the enemy without getting hurt! Once you get out of the enemy, you're fair game again.

Fixed in Super Mario Bros. DX?: Yes.
Fixed in Super Mario All-Stars?: No.
NESticle movie?: Yes.

Scale Lift glitch-fest  [Screen shots: 1, 2, 3]
You can cause lots of chaos by simply breaking platforms off of Scale Lifts. A great area for this is World 4-3. At the first Scale Lift, ride the left platform down and break it off. Jump to safety, then quickly move to the right, jumping to the Elevator Lifts. Sometimes Mario will encounter invisible platforms around the Scale Lift, either hitting his head on the bottom of one or running into the side of one. That is the most annoying part of this glitch, because it almost certainly results in death as your jumping trajectory is changed drastically, causing Mario to fall down the pit. If you happen to avoid the invisible platforms, moving quickly to the right will often mess up the Red Koopa Troopa on the next mushroom platform. Sometimes he will get stuck inside the platform, but usually he will end up walking off of it onto thin air. You can cause even more chaos by keeping the gravity-defying Koopa on the screen as you break more platforms off and quickly move ahead. Once I had an Elevator Lift drop down the pit (which I was unfortunately not able to get a movie of), and a few times scale lifts would break off and fall to the bottom of the screen (screen shot #3).
--[Found by Deezer]

Fixed in Super Mario Bros. DX?: Don't know.
Fixed in Super Mario All-Stars?: Not really.
NESticle movie?: Yes.

Mushroom through the blocks
Keep a shell sitting on an "unused" question block, and if you can get a Mushroom to slide onto that same block, hit the block and the Mushroom will drop down. Try this in World 2-1.
--[Sent in by Juan Pablo Peloso]

Fixed in Super Mario Bros. DX?: Don't know.
Fixed in Super Mario All-Stars?: No.
NESticle movie?: Yes.

Un-Fiery Mario
(This is sort of related to the "drown bug" listed down at the end.) Bring Fiery Mario to a water level. Stand on the sea floor and hold Down as you press A to swim up again. You won't be able to shoot fireballs until you touch the floor again!

Fixed in Super Mario Bros. DX?: Yes, but if you keep holding Down, it works.
Fixed in Super Mario All-Stars?: No.
NESticle movie?: No.

Minus World
World -1 (A.K.A. the "Minus World") is an infinitely-long water level, only accessible through World 1-2. Here's what you do: As Super Mario, get all the way to the green pipe at the end of 1-2. Stand on top of the pipe and smash the blocks above you. Do not smash the very last block on the right. Now, stand on the end of the pipe and face left. Jump straight up, then press and hold Right on the controller. What you are trying to do here is jump through the bottom left corner of the block backwards. If you do it just right, Mario will slide through the block and be pulled through the wall. When Mario gets to the other side of the wall, go down the first pipe before it says "WELCOME TO WARP ZONE." You will not come out in 4-1, but in -1. Yes, that's right, -1. World -1 is just like 2-2, but the pipe at the end takes you back to the beginning. You cannot beat -1, but it does give you lots of swimming practice :)
Side note: If you go down them before it says "WELCOME TO WARP ZONE," the second pipe takes you to 5-1, and the third pipe also takes you to the Minus World.

In the Famicom Disk System version of SMB, the Minus World is a swimming version of World 1-3, with gray enemies, pink platforms, and a floating Bowser. At the end, if you touch the flagpole too high, you'll float over the castle door and won't clear the level. Touch it about halfway down to be safe, and you'll drop right into the door, taking you to World -2! World -2 is exactly like World 7-3, except beating the level takes you to -3. World -3 is like 4-4, except it's not a maze, there's no Bowser at the end, and the graphics are blue instead of gray. After you touch the axe at the end, you are thanked as usual, but the Mushroom Retainer is not there. Press B, and you are taken to the title screen, where you can keep pressing B to choose a World to go to, with harder levels, exactly as if you had just beaten the game.

Fixed in Super Mario Bros. DX?: Yes.
Fixed in Super Mario All-Stars?: Yes.
NESticle movie?: Yes.

Small and Fiery
Being either Super or Fiery Mario, get behind Bowser and let him walk towards you. Jump, and try to land on the Axe and Bowser at the same time. You will defeat Bowser and move on as Super Mario. In the next World, the next powerup you'll get is a Mushroom, which will make Mario small. Next item you'll get is a Fire Flower, which will turn you Fiery, but you will remain small. Note: This will not work in 8-4.

Fixed in Super Mario Bros. DX?: Yes. I can't seem to land on both at the same time.
Fixed in Super Mario All-Stars?: Yes.
NESticle movie? Yes.

Thank you dead Mario!
Being small Mario, get behind Bowser and let him walk towards you. Jump, and try to land on the Axe and Bowser at the same time. Bowser will hit the lava, as usual. Mario will "die" but he will angle towards the Mushroom Retainer and off the bottom of the screen. The Mushroom Retainer thanks you, and you move on to the next level. Note: This works in 8-4 also.

Fixed in Super Mario Bros. DX?: Yes. I can't seem to land on both at the same time.
Fixed in Super Mario All-Stars?: Yes.
NESticle movie? Yes.

The Magic Koopa Troopa
You may already know that it's possible to stomp a Koopa Paratroopa twice in mid-air. If your second stomp is when the Koopa Troopa is 1 or 2 block heights from the bottom of the screen, he will go into his shell (duh), but it will be floating in mid-air! Of course the only way to get the Koopa Troopa 1 or 2 block heights from the bottom would be to stomp on him over a pit. For a real challenge, try to double-stomp a Paratroopa and land on solid ground. The best place I know of is in 4-3, but it's extremely difficult to do, however. So anyway, after you land on the platform, the Koopa Troopa should be in his shell and floating. Wait a while and he'll pop back out and start walking, while still floating in mid-air! (I always do this bug in 4-3, but I assume it can be done in similar levels such as 1-3 or 5-3.)
--[Found by Deezer]

Fixed in Super Mario Bros. DX?: Don't know.
Fixed in Super Mario All-Stars?: No.
NESticle movie? Yes.

Mario Copperfield
If you are Fiery Mario, you can pull off this cool stunt: Before any level begins (during the "WORLD x-x" screen), press and hold A and B. When the level begins, use the arrow keys to move Mario... and he will be "gliding" along the ground on one foot! Just release A and B and Mario will walk normally again. This also works when Mario is coming out of pipes -- just hold A and B as he is emerging from a pipe....

Fixed in Super Mario Bros. DX?: Yes.
Fixed in Super Mario All-Stars?: No.
NESticle movie? Yes.

Get stuck & drown
If you are Super or Fiery Mario, you can pull this off in any water level. Stop right before the pipe in the water that takes you out to dry land somewhere. Press and hold Down to duck, then press A to swim, and then let go of Down. As long as your feet don't touch down anywhere, you'll notice that Mario's head goes all the way through to almost the very top of the blocks! Keep pounding Mario's head on the blocks as you swim above the exit pipe. Soon he will moonwalk behind the pipe and will get stuck. The only way to get out of this is to reset the game, or wait for time to expire.

Fixed in Super Mario Bros. DX?: Yes.
Fixed in Super Mario All-Stars?: Yes, they added blocks above the pipes to make it impossible to get stuck.
NESticle movie? Yes.