Abandoned Info Page: As of the end of August 2013, the wiki for the most part is pretty outdated.
Adobe Flash: And as far as Flash games go, it's a pretty damn good one.
Ascended Glitch: As of 3.0, it is now possible to jump over the flagpole. There were certain areas in Special and Lost Levels that require you to jump over the flagpole in order to reach them.
April Fools' Day: On April 2012, the game was updated with a skin inspired by the Atari 2600. However, it also came with a massive downgrade — all the other skins were removed, there's only one soundtrack to listen to, the "Single Character Random" game mode is removed, and you can't play as Link, Ryu, Bill, or Samus (thus rendering the Classic Samus cheat useless). Version 3.0 later added the Atari skins and soundtrack to the official game, including new Atari skins for Link, Ryu, Bill and Samus.
Artifact Title: An inversion! The first iterations of the game didn't have Luigi in it (although, he was planned). Only much later on did he finally make it in, now rendering the Super Mario Bros. title accurate.
Boring, but Practical: In earlier versions, Goomba Stomp worked quicker than most character's weapons (without a Fire Flower) against most mooks; 2.0 goes around this aspect by having everyone but the Mario Bros. be unable to stomp. Fortunately, 3.0 features a cheat (which is one of the immediately available ones) that enables everyone else to stomp enemies again. Mario's better jumping tends to make him the easiest character to use, as the stages were designed with him in mind. Among the other characters, the best jumpers are about on par with Mario (though Ryu, Mega Man, and Simon all have ways to deal with their subpar jumping height.) With the timer turned on, Mario and Luigi also help get through the longer levels, being the only characters able to run.
Bottomless Pit Rescue Service: The "Bouncy Pits" cheat, which also affects mushrooms and enemies. It works on all pits, including pools of boiling lava.
Bonus Feature Failure: However, the bouncy pits cheat, on the other hand, makes Poison Mushroomsnightmarishly hard to avoid, as when they bounce off of the bottom of the screen, you can easily end up picking one up and being hurt if it bounces into you. They can also pass straight through platforms as they bounce upwards.
Cap: In older versions, the score counter maxed out at 999950. The 3.0 update later increased it to 9999999.
Special and the hard/easy maps add a powerup that increases the time you have. This powerup, like most of them, can change appearance depending on what skin you're using. In the Super Mario World skin, the powerup is represented by a green berry.
World 6-2 in Special is a Pipe Maze, which gets even more intricate on hard difficulty. This references the same level from the original Super Mario Bros. 1, which was also a pipe maze and is included in the Super Mario Bros. stages as well.
Couch Gag: The game's Start Screen always loads up a different map skin. Complete with matching skins and interface.
Difficulty Levels: As of Version 3.0, there are two types of difficulty settings: Map Difficulty and More Settings. Map Difficulty changes the levels with Easy, Normal, and Hard. More Settings, however, averts this, as it allows you to customize general game behavior.
Dummied Out: LOTS of sprites are unused in most of the characters' skins.
The Vic Viper can be found in a sheet using a flash decompiler.
Sprites from the original Final Fantasy I can be found in another sheet the same way.
Dungeon Bypass: Link and Samus (through morphball) can quickly beat 3-2 of Special by going through the small space above the warp pipe, skipping most of the level. Like most if not all shortcuts, this was prevented in the hard mode.
Ryu Hayabusa's ability to climb walls can help reach the block ceiling of some levels and skip lengthy sections of them. Most notable in Special 6-2 which would otherwise be a Pipe Maze. Subverted in some levels after finding out the blocks are unbreakable and the pipe must be reached the normal way.
World 4-2 of Super Mario Bros. Special has a hidden warp zone that leads to World ?. However, this is not an actual world. Going inside the warp pipe brings the player to a Bonus Stage called the "Exploding Rabbit Room" (according to the Exploding Rabbit Wiki). In this room, the words "Exploding Rabbit" are spelled out in coins, along with a few hidden boxes. It is also currently the only level that has the Exploding Rabbit Power-Up, hidden in a block, which gives the current character all his/her power-up (for Samus, Ryu, Simon, and Bill, it will give him or her a random Power-Up). However, this also counts as an Ascended Glitch, as this pipe was also present in Special. Although it originally just had the player wait until time ran out if entered, as the pipe didn't go anywhere.
In the difficulty settings, you can replace the Goombas with Spike Tops. They can still be killed off by Star Power or Samus' Missles, though.
Special (and the hard maps) adds Barrels and Fires from the original Donkey Kong. The former actually acts much like Spike Tops (in fact the Super Mario Bros 3 skins replace them with what seems like bulkier Spike Tops) and can still be killed by misiles, however the Fires are almost completely invincible.
In underground levels that have access to Warp Zones, the block right next to the pipe that takes you to the normal path is indestructible in order to at least have a way to play through the game normally, even as characters that easily destroy blocks.
The map skins have a "corresponding" character skin, such as Mario's sprite from Super Mario World in the map skin of the same game. This map turns World 7 into a ghost house, and if you play as SMW Mario with this on, the Ghost House theme plays. But this would seem odd if you used another skin, since World 7 by default isn't ghost-themed, right? Well, simply playing on it with another graphic skin causes the regular "ground" theme to play instead.
Normally, there's only one music per character used as a castle theme. However, when using the Zelda II map skin, if you have the music options set to "Map", the final level plays the Great Palace theme instead of the normal Palace theme.
Jump Physics: Even though the stages are all designed with Mario's jump in mind, all characters retain theirs.
Konami Code: How you can quickly unlock cheats in Version 3.0 onwards* Originally, you need to enable and disable the "Classic Simon" cheat five times, followed by the press of the Special Button. By the way, the "attack" and "jump" buttons take the place of B and A, not the actual B and A keys.. The title screen fanfare from Contra plays when you select "Enter Code" in the Cheats menu as a hint for which Classic Cheat Code you need to use.
Leitmotif: Each character skin comes with the musical score from their original game, although it can be set to match the map skin, a certain game's score or just randomized.
Marathon Level: World 8-1 is still as long as it was in the original, which means a lot of trouble for every character but the Mario Bros., as they're the only ones who can run. Fortunately, unlocking the "Infinite Time" cheat is as easy as completing the first level, providing an easy way to escape the dreaded time limit if you don't want to speedrun with the other characters in this level.
Speaking of the hard maps, one might expect the game to start out with only mild and minor changes to add a little more challenge, slowly curving into something much harder. Nope, on the first level of the SMB set there's a Lakitu at the first half, Paratroopas positioned in akward places over pits, and an ending staircase where every other block column is a tiny bottomless pit, and every other column out of what remains is a Bullet Bill cannon.
And that bonus room that serves as a shortcut to the end of the level? It now exits into the pipe before the entry pipe to said bonus room.
Remember the first Super Mushroom of Super Mario Bros? Inside that arrangement of 6 blocks ingrained forever into the collective gamer mind? Well, in Hard Map difficulty, it's a Poison Mushroom now.note The actual Super Mushroom is on the top block
Obligatory Swearing: Not ingame per self, but while playing, two videos are displayed at the side of the game, and the description on one of the videos may have a swear word in it. Fortunately, this can be somewhat avoided by playing the game in fullscreen mode.
Poison Mushroom: The Trope Namer shows up in The Lost Levels as usual, but it also shows up in the Hard Maps for the other two sets.
Also, the first loading screen advises players to support the official game releases.
Ratchet Scrolling: Removed by default, though it can be turned on in the Cheats menu (listed as "Classic Screen Scroll", which is available from the beginning).
Remake Cameo: The Hudson Bee (also known as the "Hu-Bee") is a Power-Up in Special, although it changes depending on the skin.
Retraux: The Atari skins for most characters and the Atari map layout. The choice of musical score turns it into hilarious Stylistic Suck.
Save the Princess: While originally you were always saving Toads and Peach like in the original game, the 2.1 update changes them to characters appropriate to each playable character.
Schedule Slip: The V3.0 update — featuring even more skins (including the April Fools' Day Atari skin), additional cheats, refined difficulty settings (including Remixed Level maps based on difficulty) and the Super Mario Bros. Special levels — was initially announced for the end of June 2013, but it was delayed for the end of July instead.
Schrödinger's Player Character: The Toad inside each castle and Princess Peach turn into characters/objects from the game the current player character belongs to, and the "Your Princess Is in Another Castle" response changes accordingly. Even if the new Toad or Princess are characters the player can control at any given moment.
In 2.1 and onwards, Luigi's Peach skin has her saving Mario.
Silliness Switch: There's an "Invisible" skin that gives the game the appearance of the original game, but with all possible ground, platforms and footholds removed in addition to enemies. There's also a cheat to replace all enemies with Hammer Bros. Finally, you could set all possible options to random* that would be "Music Console" and "Music Set" under "Sound Options", and "Map Skin", "Enemy Skin", and "Interface Skin" under "Graphics Options" and play "Single Character Random" mode. Each time you play this way is essentially a new adventure.
Soundtrack Dissonance: In either the Atari version of the game or when using the Atari map skins and characters in the latest version, the music that plays whenever you encounter Bowser is... "Fever" from Dr. Mario?
Speed Run: In the Super Mario Bros. 1 map set, the same shortcut route ((1-1)-(1-2)-(Warp Zone to World 4)-(4-1)-(4-2)-(Warp Zone to World 8)-(8-1)-(8-2)-(8-3)-(8-4)) works as well.
Timed Mission: Like in the original, levels have time limits by default, but it can be turned off with a very easily unlockable cheat (just beat a level).
Video Game Settings: Several map skins gives themes to the worlds, which were otherwise rather plain in the original game. The Super Mario Bros 3 skins, specifically, gives each world its own theme as seen in Super Mario Bros. 3 itself.
According to a GameXplain interview, Ryu, Sophia, and Luigi were all planned to be in the game from the beginning, but they were cut from the first release due to time and have since been reinstated into the game as of 2.0. Radd Spencer from Bionic Commando was also under consideration.
The game was planned to be ported to the Unity engine, but the port (as well as its planned multiplayer mode) was cancelled so that Jay could concentrate on Super Retro Squad. However, there will still be further updates to SMBC, including the aforementioned skin and level additions.
Simon has one to compensate for his short and awkward jump. Comes out of nowhere (Maria and later Metroidvania player characters would have a double jump, but Simon wouldn't have it until Harmony of Despair, which was released after this game).
Bass also has a double jump ability, that is unless his Quick Man skin is used.
Goomba Stomp: As of 2.0, only Mario and Luigi can do this without getting hurt.
Link can do this with a downward thrust.
3.0 introduces a cheat that allows everybody to do this.
In later versions, it's tied to the red ring power up.
Underwear of Power: Getting a Fire Flower as Samus changes her sprite to the "Justin Bailey" power-suit-less version, along with upgrading her weapon to the Wave Beam... Well, that was in an earlier version. Now, it's averted, as she gains her Power Suit when she gets a Super Mushroom (and the Justin Bailey suit is, as of 2.0, a skin).
Wily himself also gets two skins based on Mr. X and two more skins based on Quick Man.
Toad and Peach as skins for Mario and Luigi respectively. Similarly, Pit can replace Samus, Roll and Rokko Chan can replace Mega Man, and Zelda, the Old Man, and the heroes of the BSX Zelda remake can replace Link.