Bizarro Episode: This game is quite different from your usual Mario platforming game. Toad and Toadstool are playable, there's a new villain to fight with Bowser nowhere to be seen, the gameplay is slightly different, other enemies and items from the game wouldn't come back, there is no time limit, and the game turns out to be All Just a Dream in the end, something no other ending in a Mario game does.
Breather Level: World 6-2. It's a fairly short level with virtually no platforming or enemies at all. The player just has to ride an Albatoss across the stage, occasionally leaping over oncoming enemies or jumping off to get an item, challenges made easy by just using the Princess. At the end of the stage, Birdo is stuck on an elevated platform and there's one above him as well, allowing players to strike at him while basically being untouchable.
Broken Base: The third world's dungeon is seen by some as a huge difficulty spike due to the Shy Guy pots and lots of spark platforms and increased length, while others see it as the easiest dungeon in the game due to the abundance of POW blocks, the near absence of instant death traps, the ease of escaping the Phanto, the fact you get all your hearts early, and the lack of Zerg Rush enemies in the dungeon.
Bob-ombs, when uprooted, often have an extremely short fuse, damaging you if you don't throw them in time.
Blue Pansers. They shoot flames in an arc and they move around unlike their red and green cousins.
Difficulty Spike: Depending on whether or not 3-3 is difficult for you or not, this either happens there or in 4-2, a level with a very hard to find fourth mushroom, Zerg Rush Beezos BEFORE you get to the third mushroom, and some annoying platforming involving an Autobomb, not to mention fighting Birdo on ice. The difficulty spikes again in 5-3 with an area overflowing with enemies plus a tough climb up inside a tree. Then you have to fight Clawgrip, who is one of the tougher bosses.
Fanon Discontinuity: To this day, there are fans who still refuse to accept the game as a part of the Mario series, even after Doki Doki Panic was revealed to have been originally conceived as a Mario-style game.
The Princess's hovering ability. Don't have to worry about risky jumps jumping on disappearing logs when you her ability to jump and just levitate over them.
In general; Luigi breaks vertical jumping, the Princess breaks horizontal jumping (Mario's vertical jump height is actually better than hers).
Luigi's and the Princess' super jumps, when used with the run button for great distance, can not only clear certain pitfalls with ease, but they can also bypass huge chunks of some levels to reach the end faster instead of going the longer normal way. Using said shortcuts will mean passing up a mushroom or two though.
Interestingly enough, the game manual declared Toad this, due to his speed and power, saying that you will use him the most, with Luigi and the Princess only for levels that require their jumping abilities. It's probably worth noting that most Speed Runners do exactly this.
Super Mario Advance made shells rebound from walls instead of disappearing upon contact, and it now always generates hearts for every enemy it kills, making it ripe for exploitpotential.
Giant Shy Guys and Ninjis, who drop small hearts when thrown, making them an easy source of health should you find yourself taking too much damage.
Phanto. An eerie, grinning mask that shudders to life and hunts you down the moment you pick up a key and does not back off until you either drop it or use it on a door. The Advance version gets even worse - when you pick up a key, it starts out small and grows to normal size, giving it the illusion of flying in from the background, then once you throw the key away, it grows HUGE - meaning it's trying to fly RIGHT AT THE PLAYER.
The final mask gate unexpectedly detaching from the wall and attacking you. It's even worse in Doki, where the hawk head is a creepy, painted tribal mask instead.
In the NES version, you can only choose a character when you're starting a new level. If you feel like you're having too much trouble in a particular section or level with your current character and want to select another, too bad. This was rectified in the All-Stars and Advance rereleases: You can select a character every time you lose a life.
Restoring your health in the NES and even the All-Stars versions. In order to get more health, you have to kill ten enemies, after which, a small heart appears floats up from the top of the screen, which is also very missable if you take too long to get it, or worse, appears in a part of the screen where you can't get to it. If you're in dire straits and want to recover, prepare to stop do a lot of grinding, breaking the pace of the game making the game rather repetitive. The Advance remake makes hearts far more common and plentiful, plus Giant enemies spit out hearts, as well as red shells creating hearts from killing enemies, making health restoration far less of a hassle.
Serial Numbers Filed Off: Pirated versions of this game are sometimes called "Super Wonderful Mario" (on the label) and "Super Bros. 5" (on the title screen). The game is completely the same.
Sophomore Slump: Few people would call it a bad game, but where the original was the Trope Maker for the platformer genre and the next game is often ranked among the greatest games in history, 2 is mostly just considered to be a good game. It also sold fewer copies than the first and third games.note Being a Mario game, though, it's far from a categorical flop when it's still the third best-selling title on the NES; it and Zelda II: The Adventure of Link were both subject to Demand Overload when they debuted.
Clawgrip. He throws lightning-fast rocks that aren't always guaranteed to slow down enough before going down a pit. Good luck getting past him with Toad or Luigi.
Fryguy. Constantly sweeps around his room raining fireballs and delivers a deadly Kaizo Trap to those players used to hitting bosses three times and dying. Fryguy splits into four smaller versions of itself, and the more ones you kill, the ones remaining get faster. You're more likely to get swarmed and taken out by the smaller Fryguys than the lone big one.
That One Level: World 5-3 is the stuff of insanity and nightmares. A pretty long level with a blitzkrieg of Albatosses and Bob-ombs in the first part, Zerg Rush enemies underground, a hornet's nest of Sparks and Bob-ombs inside the tree, and having to contend with magic carpets and enemies on tiny cloud platforms, all leading up to an encounter with Clawgrip.
Unwinnable by Insanity: In World 2-2 where you must dig through sand, it's possible to force yourself into a dead end by digging up every sand block until they're out of your jumping range. Since the game has no timer, you're stuck there. The only way out without resetting the game is to use the suicide code (Up+A+B on the second controller). This provides the trope image. Advance also adds a vase to the bottom, and entering and exiting it will respawn the sand, making it impossible to trap yourself in the first place.
The Woobie: Birdo, the Game boy advance version makes her voice lines go from her confidently telling the players that they'll go no further... and with each incarnation (red and green) she gets more and more annoyed, and when you beat her during the green time, she just screams in pain. In fact, when you hit her during the green form, she sounds more in pain. This after she says "I'm ready for you THIS TIME!"
Vindicated by History: In 2012, Shigeru Miyamoto shocked many by dubbing this as his favoriteMario game, tied with the first Super Mario Bros. General audience reaction has been kinder towards the game in the following years, partly because it is a game that breaks the formula in many ways and introduced numerous defining gameplay mechanics.
Visual Effects of Awesome: The close-up of Mario sleeping in bed at the very end. A very convincing cartoon Mario on the NES.