Scrap Brain Zone Act 3 if you don't use the shortcut anyway. That, and its slightly less difficult predecessor, Labyrinth Zone.
It gets even worse should you fall into the deepest part of the Act. There the air bubbles are so far and few in between that the dreaded countdown is practically GUARANTEED to start haunting you, and if that weren't enough, the air bubbles actually take much LONGER to spawn than the ones found in Labyrinth Zone.
The Marble Zone is this to some players. Not only is it full of traps and tough obstacles, but it comes right after Green Hill Zone, which is much faster paced compared to this one. It's not "difficult" so much as "annoying"... wait, no, between the tricky-to-time pounding things, the lava chase, the surprise flames during the lava block rides, and the fragglemuffin' Caterkillers, it actually is kind of hard. Still not as bad as Labyrinth or Scrap Brain Zone, but it is earlier in the game.
Metropolis Zone. To make it worse, every other level in the game has 2 acts, but this has three to make the suffering longernote (in reality, this is because the game was supposed to have an extra Zone which was cut and thus the nearly completed act was included in Metropolis Zone). It also features 3 badniks who can hit you very easily when not paying attention.
Mystic Cave Zone and the damned pit. Instead of being bottomless, an unnecessary row of spikes means that if you're Super Sonic, you have to wait until you run out of rings to die. It doesn't help that this level has Everything Trying to Kill You on top of this.
This seems to have been noticed: in the official IOS remake, two changes were made to it: in the main game, the spikes are gone and you warp to Hidden Palace Zone instead of die. In time attack mode you'll still die, but the spikes are removed so it is just a simple bottomless pit.
Metallic Madness, the final level, where you are very much in danger of time running out due to its multitude of one-way doors, timed (or simply time-consuming) set pieces, and hitting Sonic with a shrink ray which only really makes him harder to control.
And don't forget Act 3, where it is harder to actually get to the final boss than to beat it.
Wacky Workbench? Combine a floor you can't stand on that forces you to jump high into areas where there are patterned background graphics that can kill you onto platforms near the top of the stage, those slowly snaking block platforms, cold blasts under most major jumps, and elevators that spin you and make you jump off oddly. Additionally, when you get thrown to the top of the stage, you have to work your way down, slowly, through the killer background, to the bottom of suspended pillars JUST NEAR the bouncy floor. At least the crushers don't actually kill you.
Carnival Night Zone, Act 2 is great fun up until you get stuck between two red and white swirling things... and you will. (On the GameFAQs message board, it's known as the Barrel of Doom.) It's actually quite easy to get past them if you know how, but the game gives you absolutely no indication on how to, causing many players to get completely stuck. One of the few Guide Dang It moments in the Sonic series. This led to the rise of a video game urban legend — back around the time of the game's release, when you called Sega's help line (Remember those?), the line's automated greeting was supposedly along the lines of "Welcome to the Sega help line! To get past the red and white swirly things in Carnival Night Act 2...."
Another thing about Carnival Night Zone Act 2 is that the level is designed to waste time; with all the bumpers and the sheer length of the level, odds are when you reach the boss you'll only have 3 minutes or so left on the clock. And of COURSE this boss is one who uses a strategy where you can only get a hit on him once every 30 seconds or so. So unless you can somehow get a lot of hits on him at once (which is only possible if you've learned the timing on Sonic's insta-shield attack, or you're willing to bleed rings in order to get those extra hits in while you have Mercy Invincibility, or if you managed to hold on to a lightning shield — which is tricky with all the water in the level) then odds are you'll time out before finishing the fight.
The beginning of HydroCity Zone Act 2 - while most of the act is fast and easy, the first few sections have you outrunning an Advancing Wall of Doom that terrified many players in their youth.
Marble Garden Zone also qualifies; uber-steep hills, out-of-control tops, spikes everywhere, hideously placed spiked maces and crushing spiked pillars, and enemies that like to pop out of nowhere. Oh, and both the sub- and main-bosses of the zone like to collapse the level on you, midway through each act.
The final boss of Act 2 is outright irritating if you are playing as Tails alone. Without Sonic to jump attack Robotnik, Tails' only option for a safe hit is to fly at Robotnik's ship from 4 o'clock to 10 o'clock to strike with his propeller tails. Robotnik's left and right side are protected by a rocket exhaust and a drill, respectively; since Tails is flying and not jumping in ball form, any strike from above will make him lose rings; and an attack from directly below is near impossible, because Tails' ascent speed is too slow compared to Robotnik's.
This is made even worse due to the fact that Tails is supposed to be a beginner character, meaning that many a kid's playthrough of the game can be cut horribly short by this and ONLY this boss. It makes you wonder why they even forced Tails up against this boss when Knuckles' boss encounter(A completely different, grounded boss in an enclosed area) was not only easily accessible outside of the normally unbreakable Knuckles Only barriers(And even so if you abuse Good Bad Bugs) but is FULLY FUNCTIONAL even in Sonic 3 Alone!
Sandopolis Zone as well, especially the second act, with the annoying ghosts and rising sand/timed switch door puzzles.
Mad Gear Zone in general, for the same reason as Metropolis Zone above.
E.G.G. Station Zone. The entire level comprises nothing but throwback bosses you fought before in previous zones/games, all of them having a "pinch mode" (read: the turned red mode); with most of them already in said mode. Not to mention that after you defeat the final boss, he pulls a Last Ditch Move that will kill you if you don't defeat him for good by attacking him at just the right moment. The best part? One of the trophies/achievements takes the difficulty of this stage Up to Eleven by having you beat the entire stage without getting hit.
Episode II has Oil Desert Act 1, mainly because of the section where you must fly over a huge Bottomless Pit near the end of the stage.
Every single one of Big's levels. Being required to complete tedious fishing levels in order to get to the final boss in what's otherwise a platformer game that's supposed to emphasize speed? Seriously? They're not hard once you get used to the system, but they feel completely out of place in the game, a very Unexpected Gameplay Change.
Have fun catching Froggy if you don't realize you have to set the lure, which tends to happen automatically with the actual fish.
The A-rank emblems, which require you to catch a fish weighing at least 2000 grams before catching Froggy, are just painful. Not only are these fish extremely difficult to catch, they're even more difficult to find in the first place!
If you're playing as Sonic, Sky Deck. Wouldn't be so bad, but the camera just wacks out, and the controls sometimes glitch up on automated sections. Easily the most glitchy level.
Attempting to complete some of the A-Rank missions as Sonic or Knuckles can be downright nightmarish. As an example, the very first level of Sonic's, Emerald Coast, is straightforward for the C and B-Rank missions. Getting through it in the two-minute time limit for the A-Rank, however, is difficult. And some levels just get worse, like the aforementioned Sky Deck and Lost World. You'll need to spam the spin-dash and memorize the level layouts to stand a chance.
Actually, Knuckles is easy if you're willing to sacrifice a life. Get the emerald pieces like you normally would until you're about to get the third one, restart, and get to those same spots as quickly as possible. The game doesn't give the pieces new spots, and thus makes it really easy to reach them within a minute (or 2 minutes on the last one).
While the emerald hunting levels in Sonic Adventure 2 are unpopular with many, Mad Space, an extremely large level with uncooperative hints and Selective Gravity, deserves a special mention. Trying to get an A-Rank on it is pain incarnate. There's a reason it took Nintendo to finally get the formula right.
Security Hall (another emerald hunting level) isn't too bad once you know it well, but until you do its very steep time limit is likely to drive you insane.
Did we mention the air necklace is past a spot where you're guaranteed to almost drown? Have fun.
Death Chamber's not too bad in the main game, although the third and fifth missions are tough thanks to that Goddamn underwater door. Knuckles' portion of Cannon's Core, though...
Crazy Gadget. Oh dear heavens Crazy Gadget. It's bad enough that the first three-fourths are jammed with Bottomless Pits and Artificial Chaos, but the real kicker is the Gravity Screw segment. It takes place in space, so the whole place acts like a Bottomless Pit, the camera is at uncomfortable angles, and there are no directions on where to go when you flip the gravity-switches, so you might as well be flipping a switch or attacking an enemy on another wall only to fall to your death. Did we mention the segment also has Artificial Chaos?
At least part of the frustration lies in Tails' mech having a health meter, in a series with a gameplay staple of collecting at least one ring to avoid being a One-Hit-Point Wonder. And unlike Eggman's mech, you don't even get an armor upgrade for it.
The levels Final Rush and Final Chase of Sonic Adventure 2 are some of the most irritating levels ever made:
You play Final Rush as Sonic, and you start out having to grind and jump between floating surfaces. The kicker: it's almost always over a bottomless pit, there is always Camera Screw at the worst possible moment, some of the surfaces will let you got RIGHT THROUGH THEM, and gravity can change its mind several times a second!
It gets even worse in the fourth mission (time limit). The level is set up in such a way that it actively encourages you to try taking faster routes. However, these routes frequently invoke the camera screw and can really make gravity pull SIDEWAYS! Even worse, it's a long level with tons of bottomless pits, so one slip-up and you die and have to restart from the beginning.
You play Final Chase as Shadow, and you start out grinding before coming to a platform. The bulk of the mission is about going between spinning gravity drums and platforms. Again, bottomless pits abound, and the most common enemies on the level are Demonic Spiders (the Artificial Chaos robots).
The level itself isn't too hard on the first mission (reach the goal). However, when you do it with a time limit, all the problems from Final Rush come into play except for the multiple pathways. There are still the issues with falling to your death, Camera Screw, capricious gravity, and the Demonic Spiders. Not to mention the sheer length of the level and the fact that dying means you have to redo the whole damn thing.
These levels themselves in some ways though mildly avert this trope. They are partially only as hard as you make them, so if you are cautious and go by the default and easiest path, they aren't too hard. However, god help you if you should attempt to use an alternate route.
Let's not forget the "Hard Mode" versions of Route 101 and Crazy Gadget.
The hard mode version of Route 101 is so difficult you cannot beat it with anything less then an A-Rank. You will always beat it with 1 or 2 seconds to spare if you are really really good. If you are not really really good? Oh no! I lost him!
The hard mode version of Crazy Gadget takes Camera Screw and Interface Screw to a whole new level. Not only do you get the picture inverted and the controls messed up, the hard mode version forces you to make some near-impossible homing attack jumps over bottomless pits and forces you to bounce up to rails you grind while everything is wonky. Did we forget to mention the dramatic increase in the Artificial Chaos population? In normal mode you only encountered three of the exploding variety of Artificial Chaos. In hard mode, they are everywhere. Add it all together and you get the hardest mission in the game.
Meteor Herd: A large and sometimes confusing stage that wouldn't be quite so bad if it weren't for one factor: Meteorites striking all over the damn place, and sooner or later, one of them will be headed your way, and you probably won't see it until right before it hits you. Even the soundtrack tries to warn you about it.
The trolley ride in Bullet Station. This entails controlling a trolley car through a Death Course with lasers and spiked balls everywhere. If you get hit once, your speed is drastically decreased and you lose the ability to control it. Twice and you lose the ability to steer, leaving the trolley to travel on a fixed path.
The Chaotix version of Mystic Mansion has you putting out torches throughout the mansion. What makes it so hard? THAT GODDAMN SPIDER WEB. Okay... you grind across the web, and Trial-and-Error Gameplay is in full effect; you have no idea if the path you grind down leads to torches or a Bottomless Pit. And if you're doing the second mission, the torches you need to put out are in the middle of the web and you need to jump off with good timing to avoid getting burned or falling out. Also, if you miss a single torch in either mission, you go all the way back to the beginning of the level. It certainly doesn't help that most levels in Heroes are much longer than Sonic standards.
Team Chaotix's second mission on Bingo Highway. Thought collecting ten casino chips was difficult when you are a pinball on a board riddled with instant death holes? Good, now collect all twenty of them!
Even worse is Team Dark's second mission on Rail Canyon to destroy 100 enemies in less than twelve minutes. This sounds easy until you realize that the level lives up to its name quite well, and about eight or more minutes will be spent grinding down rails with very few enemies to defeat, which means you have to hurry if you want to find 100 enemies in time, to the point where you will probably have to make it to the goal ring which will send you back to the beginning of the level so that the enemies would respawn. It's like running a level twice in 12 minutes and destroying all of the enemies in your path at the same time.
If you're playing as Team Sonic or Team Dark, Lost Jungle is a nightmare. If you're trying to get the Chaos Emerald, good luck trying to swing on vines while avoiding a giant alligator trying to eat you!
It was considered by some to be annoying enough to begin with, but the level that really takes the hatred is Cosmic Fall, which forces you to jump between moving platforms floating in space. It wouldn't be so bad, except that the camera seems to be designed specifically to screw you over; every single time you jump the camera will spin randomly, making it impossible to see where you're going to land. And it has a time limit, too.
Any mission where you have to destroy a vehicle before it gets away is outrageous, particularly the Dark mission of Air Fleet and the Hero mission of Iron Jungle. Every single shot counts, some vehicles can retaliate, and God forbid you die; you reset to the last checkpoint touched, but the target vehicle doesn't, meaning that by the time you respawn, the vehicle will be so far ahead and so close to escape you may as well restart.
These missions can be made easier however, if you wait till you beat all the endings and get the Shadow Rifle. Once you get to a spot where you can fill up your Hero or Dark Gauges (Which is easy on Air Fleet) and gain unlimited ammo, you can use the rifle to take down the vehicles in no time and get an easy A.
Central City is the only level in the game to not have a goal ring; instead, both missions involve you detonating/disposing of bombs. Thing is, the level design is confusing, with the Dark and Hero paths overlapping and criss-crossing, and it is easy to find yourself going around in circles and unable to find where the next bombs are. That wouldn't be so bad except both missions are timed. Eight minutes doesn't seem so generous when you don't know what the right way through the level is!
Mad Matrix, especially the Dark mission. It's painfully easy to get lost in the mazelike circuit that connects the towers; on the Dark mission, you have to spend pretty much the entire level in that circuit, as it involves detonating bombs that are in the circuit. And there are no less than 30 bombs to set off, and you pretty much need to go through every last inch of the circuit as the bombs are distributed pretty evenly.
The only good thing about Mad Matrix is if you do the Dark Mission, you're guaranteed an A as long as you don't kill too many Aliens, no matter how much time you take. Be ready to spend up to an hour doing it, though.
The two ARK stages, The Doom and Lost Impact, are incredibly frustrating.
The Doom has you either killing soldiers or saving researchers. Regardless of which mission you pick, the soldiers are very aggressive and will rush at you at the drop of a hat. In the Dark mission, you have to take down every last one, and in the Hero mission, you'll lose points if you kill them. Additionally, the stage is very maze-like, and while there is a map, it's hard to read. On the mission with the researchers, there's a glitch that can make it Unwinnable by Mistakenote the item you need to heal them can get suspended in mid-air, making it impossible to pick up if you don't have the Heal Cannon. Incidentally, this is the only level where that weapon is actually useful.
Lost Impact is long on top of being maze-like, and there's no map here. The Hero mission has you exterminating all of the Artificial Chaos, and you have to scour all the indoor sections if you are to get every last one; there's nothing worse than spending 20+ minutes on the stage only to realize too late that you missed one. Additionally, there's a lot of them on the paths of the GUN Rails, which can't slow down or stop while Shadow is manning the gun, and some might hide in shadows. The one upshot to all this is that the soldiers here actually don't attack Shadow at all and sometimes actually assist in taking down the Chaos. This level has been perfectly described by Lewis from BrainScratch Commentaries: "Imagine three dimensional except badly designed Super Metroid where you can't miss a single Missile Tank and you have this level, only the Missile Tank shoots back.
Space Gadget. This level has gravity-changing fields that you fly into which affect the controls in...weird ways. Sometimes it seems like the game can't differentiate between two different gravity directions, and so you'll end up doing things like light-dashing backwards even if you're facing forwards. If you're doing the Hero mission, you're put on the clock and you have just five minutes to clear it.
Black Comet. It's pretty long, the GUN mechs are very aggressive, and a lot of time is spent on the Air Saucer over some substance that cannot be touched. The Saucer has rather slippery controls and you can only shoot forward on it. And god help you should you lose the saucer, in which case death is pretty much the only option. And on the Dark mission you have to kill every last GUN mech.
And even Radical Train pales in comparison with End of the World: combine mysterious sucking instant-death spheres with brutal platforming, and you have a recipe for pain.
Some of the combinations of characters and stages for End of the World are ridiculous, too. Tails in Crisis City? Silver in a quicksand-heavy portion of Dusty Desert? The former also has the instant-death spheres hanging over a pit that you have to fly over. And they're the vacuum variety. Argh! It's also a really good thing you can glide over most of the stage in both Knuckles' and Rouge's sections, as they're nigh unplayable if you try to beat them "legit". And then in Shadow's section (the very last one, making it immensely irritating to S rank), the orbs can appear literally in the middle of the thin paths you're on and require some well timed and well aimed jumps.
Aquatic Base. It's not as difficult as Radical Train...for the most part. Then you get to the metallic sphere hanging over a Bottomless Pit; you jump on the sphere and (attempt to) ride it to the other side of the room. It takes longer than it should to get it to start or stop moving, and if the sphere takes even one hit, it pops and you fall to your death. The ending portion of the stage also bathes everything in a red glow, making it impossible to see some of the enemies.
Speaking of Silver and Dusty Desert, his actual portion of that level has some puzzles that involve knocking balls into holes in order to open a door. The problem with that, especially on the second note of two, fortunately is that you can only move it with your normal attack which has next to no range, you only get so many attacks, and sometimes the amount of attacks you have left will decrease FOR NO REASON AT ALL! And the second puzzle involves sending the ball down a very long corridor and it is very much a race against time; you have to get the ball in the correct hole before it blows up and before you blow up in rage!
Sonic's Crisis City is a fucking nightmare, especially in the on-rails segment, in which the game can randomly glitch out, pushing you to the right for no reason, and where it's all but impossible to avoid taking hits because there's literally so much debris on screen.
Shadow's version of Crisis City has an infamous section where you're supposed to homing attack multiple enemies in a chain, only you'll fail and fall into a bottomless pit until you know to hover slightly higher and skip that enemy to hit the next one. The Chaos Snap can skip this, but is prone to just glitching you into the pit at the other side, for some reason. Luckily, other than that it's mostly a Marathon Level and not a particularly difficult one, but that one section is a tricky bitch.
The snowboarding segment of White Acropolis is also horrible, and in the part with the giant snowball, you can get stuck on a wall and can't get out.
Shadow's version of Kingdom Valley deserves a mention for being a hell of a wake-up call for a second stage in his storyline. First, you play as Rouge where you find three keys to open up the next pathway, only you're without a radar and without hints. And then, there's Shadow's hovercraft section where you have to avoid the collapsing pillars that are instakill on impact; the kicker? the camera doesn't change to let you know where each pillar will fall, leaving you to get blindsided.
Silver's Kingdom Valley isn't any better. It goes on for an eternity, and generally has loads of enemy fighting segments, only half of them are the yellow robots that shoot away dropped rings, making you easy pickings for other enemies. The very end pits you against several of these and the blue robots who aren't much better as well. The only reprieve you get is that you get to play as Sonic for a short time.
The End Of The World from the game's Last Story definitely qualifies as well. In it, you are forced to play as every playable character in the game except Sonic, Who is killed by Mephiles in the cutscene before this level, and Blaze, Who performed a Heroic Sacrifice at the end of Silver's story, in a Marathon Level composed of altered versions of 7 of the game's previous levels, determined to leave you tearing your hair out at every turn. The level's main gimmick is these cheap time portals that open up randomly across each part of the level and try to suck youin, and if you touch them, you're dead, no matter how many rings you had on hand. This is especially a problem for Silver, who is the slowest of the playable characters and can be sucked in much more easily than the others. And to keep the time portals from opening, you must hit special statues sparsely scattered across the level. Add in an onslaught of enemies, and the game's already poor level design and character controls, and you have a recipe for pure frustration.
Eggmanland, ESPECIALLY the 360/PS3 version, where you're forced through 45+ minutes of non-stop Nintendo Hard suffering. The stage seems like a normal (if incredibly difficult and requiring pitch-perfect timing) daytime Sonic level at first, but then you hit the first hourglass and switch to Werehog form — and that's when it hits you that you're going to be switching between Sonic's two forms a lot during this level, and given that Werehog levels on average take about 15 minutes, you can tell this is going to take ages before you finally hit the goal ring. Indeed, given the number of times you switch between Sonic's forms in the final level, it's really something like five or six levels in one. Even subsequent runs, after you've learned the stage, can take upwards of 20 or 30 minutes. To add insult to injury, the very last challenge (after some insane platforming, difficult combat sections, and instant death QT Es which are hard) in the gauntlet from hell is a Werehog brawl against two Dark Titans. Eggman really didn't want you getting through this one.
The Wii/PS2 version can also be a pain in the arse — instead of one Marathon Level, it's split into one Sonic stage (and subsequent missions) and five Werehog stages. The latter can actually be somewhat enjoyable, but the day stage is flat-out ridiculous at times.
It's just one bottomless pit after another in Adabat's Werehog levels. The last act in the Wii version (HeavenlyRuins) can be brutal, particularly the battle at the endnote Waves of Fright Masters, set over an area comprised mainly of floating platforms that drop after you step on them. It's quite easy to fall off, and lord help you if you want to climb up and collect the secret item while all of the Dark Frights are dogging you.
Then there's the daytime level of Holoska in the X360/PS3 version, specifically the parts where you have to run on water, but you have to make sure to hit almost every single dash panel to not end up drowning.
These stages are easier if you resort to Pause Scumming since the QTE prompts aren't hidden when you pause. If you pause the moment the prompt shows up that gives you more time to see it and nail hitting the correct buttons when you unpause. The Egg Cauldron fights can still be tricky due to the amount of stuff being thrown at you, but it makes them more manageable.
The DS version brings us Asteroid Coaster. It is the last of the 6 main levels, and by far the cheapest. There is this green goo everywhere which acts like a bottomless pit even if you're nowhere near a bottomless pit. The purple wisp is good to use but if you run out of it (it hovers and sucks stuff in) you'll just fall in the goo. Often you also get chased by giant dinosaur heads, which instantly kill you if they touch you. Worst part is, sometimes these sections have the "press R to slide under the barrier", which you would never get first time, same with a point where you have to jump up or get owned. And then there's the falling rocks which hurt you and impede your progress, unless you're boosting. And sometimes you'll have to use the slide then as well repeatedly, which runs the risk of you getting hurt. Also there's a few actual bottomless pits which appear at the worst times.
Act 3 of Planet Wisp in the Wii version can be annoying towards the end. It's incredibly easy to either miss the small platforms, or have the Cube power run out while you standing on the solid blue boxes, leading to you plummeting into the toxic waste to your death. It's actually a really short level, but having to do this part over and over again (as well as several of the Red Rings being all over that particular area) can ruin your score, because the timer doesn't reset to what it was at the checkpoint when you die.
A few irritating missions, but for the main levels, Crisis City Act 2 (the Modern Sonic act) is particularly tricky first time due to bottomless pits and a lot of lava, as well as enemies being sometimes difficult to hit. It culminates in a section where there's geysers all over the roads and a tornado throwing cars and rocks at Sonic. Act 1 (the Classic act) can also be rough due to the tornado that eats you up if you're within it at the wrong time, and having to jump on irregular platforms including cars and parts of buildings while a strong gust blows you back.
Planet Wisp is also challenging, but that's more a case of being a Marathon Level than actually being ridiculously hard. Act 1 does have its issues though, mostly because it's 90% reliant upon the Spike Wisp from Sonic Colors, only it handles a lot worse than it originally did in that game.
There's a side mission where you have to Homing Attack a music note back and forth with Vector... it's much harder than it sounds, especially when the note speeds up and flies to the back of the arena while you've just touched the ground on the opposite side.
The game in general can be quite Nintendo Hard in the latter half, but Lava Mountain Zone 2 really takes the cake. You spend the entire level grinding on rails, and you have to be REALLY precise with the jumps you make. If not, you'll spend a lot of time plummeting into the abyss, or ramming into a cart of explosives that can instantly kill you. If that wasn't enough, you also have moving doors that'll kill you if you aren't fast enough to reach them before they close. That power-up that lets you skip to the next checkpoint seems mighty tempting now, doesn't it?
Frozen Factory Zone 2 can also be a pain in the arse. Are you good at Star Ball Rolling in Super Mario Galaxy? Hope so, because the whole level is like that, even in the boss fight! You don't get rings until you touch a checkpoint while having rings stuck on the ball (fortunately, it doesn't matter if the checkpoint has been used or not), so you can get one shotted easily. The whole level also takes place above a bottomless pit on smallish platforms. And there are bomb enemies that, if they explode while in you, send you hurtling into one direction. And there are yeti who bounce you away from them (some are stationary and don't try to hinder you themselves, but big ones will run toward you). So you are going to fall. A lot. And may God help you if you go after Red Rings - the last one requires you to hit all the snooker balls you come across. You only get one shot and once you get past it, you're immediately flung into a checkpoint, so if you ballsed it up, you have zilch option but to restart the level all over again.
So you've managed to get past Lava Mountain 2. You're feeling pretty good and psyched to finish up the last couple of levels. Then Lava Mountain 3 comes along and shows you that the suffering isn't over yet. The 3D sections of the level shouldn't be too much of a problem, but the 2D sections can really test your patience. They're vertical shafts that each lead up to a member of the Deadly Six. All of the sections have instant-kill lava rising up beneath, so your platforming skills better be good if you don't your lives to go down the drain. If that wasn't enough, each of the Deadly Six can potentially be That One Boss. Zeena requires precise timing of the Homing Attack if you don't want to hit the spikes on the ceiling, Zor can knock you into the lava and Zavok's second form is by far the hardest boss in the game. Zavok is the last obstacle in the level, and if you end up losing all your lives to him, you have to start the entire level all over again. Have fun.
The portable Sonic games have their own brand of scrappiness. Case in point:
Labyrinth in the Master System/Game Gear version of Sonic 1. As if the original wasn't evil enough, they mess with the palettes for the underwater sections, and Sonic actually feels slower than in the original.
Scrambled Egg from Sonic 2 (Game Gear and Master System). Unless you know the layout of all the vacuum tubes, it's essentially Trial-and-Error Gameplay at its worst.
Electric Egg from Sonic Chaos. Electrified floors, high-speed vacuum pipes that lead to suddenly-dropping platforms, and a mesmerising tileset that may distract you until it's too late.
Robotnik Winter from Sonic Triple Trouble. Apart from some slippery flooring and nasty speedtraps, the updrafts you need to use to climb up vertical shafts are notoriously unreliable, which often results in plummeting into an icy chasm.
Tidal Plant is even worse, as it takes place almost entirely underwater, it has a tricky section where you have to navigate a giant bubble up past spikes and enemies, and it's extremely easy to get hit and have to start the section all over. This is notably easier with Tails because he has the Sea Fox, but not by much.
The final level in Sonic Spinball is utterly horrendous; all the required Emeralds are heavily guarded, there is virtually no safe ground below you, the climb up to the end boss is a nightmare, and the end boss itself is actively trying to (and can easily) knock you back down to the bottom of the stage. Compared to it, the rest of the game is a cakewalk.
Blue Marine in Sonic Blast. It's entirely underwater with no dry land, air bubbles are spaced far apart, and the tubes can be very confusing to navigate.
Altitude Limit. Lots of instant death lasers that act as bottomless pits, long acts, sections where you float upwards on rocket platforms avoiding spikes and enemies, and a section in each act where you have to jump up areas of falling platforms.
Sonic Rush Adventure has a pretty decent difficulty curve, but anyone striving for 100% Completion will shake their fist remembering the snowboarding mission. That level was awesome on its own, but with limited controls and a complete inability to stop moving it really feels like Fake Difficulty... that and the only way to figure out each checkpoint is by trial and error.
And that's just for missions. The regular game gives you the hell that is Sky Babylon Act 2. There is fire everywhere (you need to be careful as Sonic, though Blaze can just run right through it) and all of the hardest obstacles are immediately before the end of the stage, and dying more or less resets your score. This gets even more difficult when you realize that this stage has an obstacle that kills you instantly, in the form of a zig-zaggy purple line, whether or not you're holding rings, collecting rings, using a shield, or invulnerable. In most places this would be less as important as it appears over bottomless pits, but at this point they surround incredibly touch sensitive rising platforms, enemies that both move and shoot, and the usual falling platforms. Even getting a good score on this stage is harder, as score and time requirements are harder than the last stage.
Dino Jungle. It feels so out of place, and that egg mission doesn't help...
First, take a level which is literally a giant, bottomless pit, then add some visually interesting platforms, lots of grind rails, strong winds, and for good measure, toss some spiked Air Launchers among regular ones, so that the player has to learn where the lethal ones are, lest they want to see Sonic fall to his doom. Finally, add a couple of tricky platforming sections, combine it with a fiddly control scheme, and ta-da!: You have the Levitated Ruin levels from Sonic and the Secret Rings.
The first Dragon's Lair stage from Sonic and the Black Knight. Fall away floors to bottomless pits that are impossible to see coming. Endless swarms of enemies whose sole purpose in life is to block all of your attacks and then knock you into said bottomless pits. Giant armored titans surrounded by those endless swarms of enemies whose sole purpose in life is to knock you into the bottomless pits. Oh, and there's a time limit.