How am I supposed to move this thing? I know there's something under here...
As seen to the right, Sonic 3 & Knuckles, that infamous barrel in Carnival Night Zone, also known as "Barrel of Doom" (solution: stand on the barrel and press UP and DOWN on the D-pad in sync with the barrel's bobbing motion to shift its weight). This was such a bad case of the trope that Yuji Naka publicly apologized for it in 2011 at Summer of Sonic in London.
While the down key is used frequently in gameplay, the up key has little to no use in the game elsewhere. The up and down keys also appear to be non-functional while standing on a barrel. Pressing up or down does not make Sonic look up or duck down like he does elsewhere. If the barrel is stationary, pressing the up or down keys will do nothing. If you tap the up and down keys randomly, you're not likely to notice a change in the barrel's velocity.
Jumping on a barrel makes it move. In fact, it is the only thing a player can do to a barrel that is guaranteed to give instantaneous feedback. It doesn't help that carefully timed jumps on any other barrel in the zone will be enough to pass them.
It is only just possible to get past the Barrel of Doom by jumping on it until it falls low enough that you can spin-dash under it when it pops back up. Players that could almost make it would believe they were doing the right thing, just not well enough. Plus, this method would often leave you with not enough time to reach the next checkpoint.
That barrel is the only barrel in the zone that cannot be skipped. You will run into it, unless you're playing as Knuckles.
If you read the manual, and saw the tip about how Sonic would sometimes run into traps that were completely inescapable except by waiting for time to run out or resetting the game, chances are you wouldn't realize that it was actually handwaving the rather large number of glitches that the player might encounter, and instead think it was referring to That F-ing Barrel.
At first, this wasn't even in the guides.
They seem to be hoping that pressing down and up like that would feel natural to the player, like how most people pressed A when they wanted to catch a Pokémon, or pressing B to run.
Finally, the fact that merely standing on the barrel makes Sonic spin around vertically, which in any other situation would imply that he can't be controlled beyond making him jump off it, discourages people from actively trying to figure out what they need to do.
The barrel's many frustrating features can all be chalked up to one thing — it's not actually a puzzle. It was simply intended as yet another of the myriad obstacles in Carnival Night Zone Act 2 that eat up your precious time, and the devs failed to consider that figuring out how to move the barrel would ever be an issue.
To reach the Robotizer in Zone 1 of Wacky Workbench in Sonic the Hedgehog CD, you must stand on a block that looks like a crusher and let it slam you against the ceiling. Rather than crush you, it drops you into a secret area (although it looks very similar to the realSmashing Hallway Traps of Doom found later in Metallic Madness).
Sonic the Hedgehog (2006) had many omissions in the game manual; the game was severely rushed, so several of the things in the manual weren't actually in the game. In Shadow's Kingdom Valley, in one section you play as Rouge, and have to find 3 keys, 2 of which are relatively easy to find. One of them, however, is in a tower, which you can only get into by climbing the tower and breaking one of the stained glass windows by planting a bomb on it. Sounds simple, right? The problem is, Rouge's bomb-planting move isn't listed anywhere in the game manual, and the game itself doesn't even mention that specific move. Before this point, you most likely won't even realize that you even have that bomb-planting move, let alone know how to execute it.
Like most Sonic games, Sonic Advance 2's true ending can only be seen if you collect all 7 Chaos Emeralds. However, to get to the Special Stage to even attempt to get a Chaos Emerald, you had to collect all 7 of the Special Rings hidden through a level. Unfortunately, as a later Sonic game, it wasn't really known for its exploration and most players would end up running right past them. It doesn't help that backtracking is pretty much impossible and players would either have to memorize an entire level to get them or get the game guide with the detailed maps. And you lose the rings you got if you die. Guide Dang It indeed...
Sonic Rush Adventure: As opposed to nearly every other hidden island that is hinted at where there is shallow water, there are two that you may have to scour the entire sea map for, as there is no sign that they're at the very top of the map, far away from any other island. Also, That One Boss Ghost Titan has one of the most absurd strategies behind it ever.
In Sonic Heroes, there is at least one point (Extra Mission for BINGO Highway) with Team Chaotix where you have to use Leaf Swirl to turn Espio invisible so he can pass some lasers. At no point in the game is it mentioned that turning Espio invisible makes him able to pass through lasers.
Shadow the Hedgehog doesn't have many moments like this, with one notable exception. The Hero mission for Space Gadget is just the Neutral mission on a time limit. If you want to get to Cosmic Fall from this level (by clearing the Neutral mission), you have to run out the clock on the Hero mission first, otherwise the game will count it as you passing the Hero mission and instead send you to Final Haunt. This is the only stage where something like this happens.
Sonic Adventure has a few Adventure Field emblems that can be tricky to find. One of them requires flying over a large, seemingly empty space as Knuckles — and the emblem itself won't show up because of the draw distance until you're actually close to it. Another requires you to know that Tails' tail-swipe attack that he performs when standing still, and only that attack, has the power to cut certain specific types of grass down, which you must then use in an out-of-the-way area of Station Square to reveal the Emblem.
A strategy guide for Super Mario Bros. 3 mentioned that one could get a whistle by dropping through a floating white block in stage 1-3 and then running behind the ending curtain. Only one problem: The guide didn't specify how to drop down... and holding down the 'down' button for several seconds isn't something that's immediately obvious.
All three of the whistles are like this, really. One in the first fortress has to be obtained by flying up, over, and around the ceiling, then finding a door in the dark (the camera doesn't follow you over the ceiling, so you have to grope around with the up button). The last whistle is on world two, the desert, and you have to break a rock that was delicately placed to blend into the background; without seeing something like The Wizard, your only clue is to Try Everything (because up until that point you aren't told what the Hammer actually does, and there's no penalty for trying the Hammer on every square).
Super Mario Sunshine uses this trope in the form of Blue Coins, 10 of which equal 1 Shine Sprite in an exchange with an NPC. While they are not needed to beat the game, they will drive 100% completionists batty as they will search every nook and cranny, squirt water at anything that moves or doesn't move, and do all this for EVERY EPISODE IN EVERY LEVEL.
Also, to get one of the Shines, you have to stand at a certain point in one of the levels, look straight up, and spray water at the sun. After you spray it, a Shine will pop out.
In another mission in the same area, you need to find a certain point and spray water at the moon for a Blue Coin. Both of these are hinted at by villagers, but still.
At least two secret Shines can only be found by spraying normal looking SAND in apparently random places with water.
In addition, a secret Shine involves going into a remote corner, finding a tiny yellow bird, and spraying it for several minutes (since it's moving and flying about constantly) before it transforms into a Shine. There is absolutely NO indication that you ever need to do this.
Once you've figured out the general pattern (spraying blue birds with water gets you Blue Coins, spraying yellow birds gets you Shines, and in one level, spraying a red bird gets you a Red Coin), you can find all of the related secrets pretty easily. It still counts as a Guide Dang It, however, because nowhere in the game is it ever indicated that spraying birds with water has any kind of point to it.
Other Blue Coin Guide Dang Its: Yoshi can eat the bees that emerge from the beehives in certain levels. This in itself is something that a player is likely to discover. However, to get a Blue Coin, you have to knock down the beehive with Yoshi juice and then have him eat all those bees as well, which is not something that's likely to occur to the average player (in part because knocking down a beehive would seem to be a bad idea).
In Ricco Harbor, you have to spray a normal-looking solid wall in order to make a blue shine sprite symbol appear, which then yields a blue coin. It is not hinted at, and the only way to likely find it without a guide is by spraying said wall entirely on accident or while messing around.
In Super Mario Galaxy 2, they barely mention Grandmaster Galaxy or how to unlock it. They also never hint at where any of the Green Stars are. For the ones that aren't sort of hidden in plain sight or just out of vision but still audible, good luck finding them.
Here's a fun example from the fifth boss galaxy. The second star can only be found by shooting out of the cannon on the blue and purple sphere planet not toward the next planet, but really far and up to the left. You probably never thought of looking over in that direction.
Getting the first episode of Grandmaster simply requires getting all the other stars in the game, which is intuitive enough. Getting the second episode requires putting 9999 Star Bits in the bank, which is hardly hinted at all.
In Prince of Persia, to kill your shadow, you have to Sheathe Your Sword, which causes the shadow to do so as well. (He's attacking you out of fear; once he sees that you mean him no harm, he's happy to return the favor.) Then simply walk or run toward him until you recombine. You do have to wait for the flashing to end, but you don't have to run off the platform; it's perfectly okay to jump (which might actually be more appropriate, since this is supposed to be a "leap of faith").
There's also a minor one at the end of Level 8, where you find yourself stuck behind a door, which can be opened only by a button on the other side. What you might think is the solution — get in and out of that room before the door closes. The actual solution: Wait for a mouse to come and press the button. Fun...
In Prince of Persia 2: The Shadow and the Flame, the player must die in a mundane way, killed by an easy-to-defeat Mook at a specific spot, while there are several, much more extravagant ways to die around (particularly falling into Bottomless Pits) in order to obtain the titular Flame. A lot of people never figure this out and skip the level using cheats. Contrary to popular belief, the sword in the ruins isn't one of these: true, touching it appears to kill you, but it also immediately fades to a cutscene explaining more backstory.
This probably isn't any consolation, but the tipoff was supposed to be the huge sign you passed that said "He who would steal the flame must die". That was a double entendre (i.e. try to take the flame = you die, die willingly = you get the flame). If nothing else, getting burned to a crisp or falling to your death 30 times should've at least prompted you to try SOMETHING different (something a theme throughout this series).
Lets not forget the final level, where you need to turn into the flaming shadow in order to beat Jaffar, by turning left and right repeatedly. Most, if not all players discover this by accident while playing around with the prince in one of the last levels.
In fairness, this is mentioned in the instructions, and it even tells you the exact requirement. The hard part is remembering it at that point in the game. Oh, and meeting the requirement. And, quite possibly, getting killed by Jaffar a dozen times.
Also the fact that you only survive it if you have enough life; there are potions available on one screen to increase it sufficiently, but it's not exactly obvious that you can climb down to there off one platform when the ones slightly further along are Bottomless Pits.
Some of the life upgrades in Prince of Persia: Warrior Within were nearly impossible to find. One is found early in the game through a hole in the ceiling. The box which can be used to access it is behind a breakable gate - except that you don't have the gate-breaking sword yet, and if you haven't played the previous game, you wouldn't know this gate might be breakable. Instead, you would have to backtrack to that part of the game when you get the sword. Another life upgrade can only be accessed by descending down a very deep chasm, which seems bottomless from above.
There's also a Block Puzzle when you first enter the library which requires dragging one of the mirrors away from the wall to reveal a crack through which your companion can sneak to activate a lever later in the puzzle. The problem? The puzzle can be passed up to the point where the lever needs moving WITHOUT dragging the mirror out. Meaning that you get most of the way through and then can't figure out where on earth you went wrong, nor why your stupid companion is just standing there instead of pulling the damn lever. Guide Dang It. Heck, even some of the guides don't make it properly clear...
In order to get to Rusty Bucket Bay in Banjo-Kazooie, you need to transform into a pumpkin and go under a gate in the graveyard room where you enter a building which results in other things happening, but the gate doesn't look like it has a hole.
Banjo-Tooie has several unduly annoying Jiggies. The worst and most infamous of these is Canary Mary's race in the final level, Cloud Cuckooland. It's a button-mashing race. The Guide Dang It part? You're not actually supposed to mash the buttons. Canary Mary has Rubber Band AI, and if you speed up, she speeds up proportionally — meaning that if you get too fast, she becomes impossible to beat. Making this even more fun is that you raced her before in an earlier level, where you could mash your way to victory somewhat easily.
What may be worst about this is that Mary's finish line is actually before yours, meaning that if the race ends with you ahead of her, it's still entirely possible for you to have lost.
The Xbox Live Arcade port added a new Guide Dang It: Stop 'n' Swop II. The first four objectives are simple enough: hatch all of the original Stop 'n' Swop eggs and collect the Bronze, Silver, and Gold eggs. However, for the remaining three objectives, you need to beat every boss under a total of 15 minutes, become each and every one of Humba Wumba's transformations, and finally, kill yourself 40 times during boss battles.
Many players also have trouble with the Jinjo in Spiral Mountain under the waterfall. Most players wouldn't even think to look in Spiral Mountain for the final Jinjo.
Also, Grunty Industries is an entire world of this trope. Just for some perspective, when you first enter the world, you find yourself outside the factory with the main door sealed shut. An uncrossable marsh surrounds you, all you can reach is a handful of pickups, an unkillable battery enemy, and a switch to add the world to the inter-level train network. That's right, not even a hint on how to get into the level proper! Tip: That train station isn't outside, either.
Many of the Secret Bonus Points in Dynamite Headdy require you to perform extremely counterintuitive or un-obvious actions, and there are no hints anywhere.
In Mega Man 5, the letter plate in Stone Man's stage is hidden in a secret room behind a destructible piece of wall. Unfortunately, that piece looks only slightly different, so you are very unlikely to notice it unless you're actively looking for a secret room already. There are more secret rooms in this stage with generic items, one of them being a rare Mystery Tank. Finally, there is an extra life in plain sight within a wall, but no part of the wall is destructible; there is an invisible passage, but it's too high up to reach it simply by jumping – you have to use Rush Coil to reach something you don't even know is there.
In X3, who the heck was supposed to guess that you had to get the Arm upgrade and use the charged Triad Thunder in order to drop the rocks in Tunnel Rhino's stage?
And even that's more intuitive than the other place where the charged Triad Thunder is required... the beginning of Crush Crawfish's stage, where it can destroy a floor leading to a Ride Armor capsule. There is no indication that the destroyable area is any different from the rest of the floor around it.
To acquire the most powerful armor in Mega Man X5, you are required to drop X down what appears to be a bottomless pit in one of the final stages; if you're on the correct side of the shaft, you'll fall through a false wall into the room with the armor in it. The kicker is that the armor won't be there at all if you played through the stage with any of X's other armors, and there's nothing in-game to suggest this is the case. To be fair, the game will allow you to collect the armor with Zero regardless (although if you complete the stage with either character and neglect to pick up the armor, it's Lost Forever).
The hidden ultimate upgrades in X1-X3 (The Hadoken, Shoryuken, and Gold Armor) are all likewise obtuse. And except for the Hadoken, they are also Lost Forever once you complete that level.
The Gold Armor is doubly bad because, while the capsule to get it is not terribly hard to find, the armor itself can be rendered Lost Forever by getting any Upgrade Chips earlier, something you wouldn't know before reaching the Gold Armor without a guide.
Getting the Z-Saber in X3. You have to bring Zero into a mini-boss fight in one of the final levels and defeat it with him, causing him to get damaged and hand his Saber over to X; said Saber is an added final charge level and can swipe off half of every boss's health other than the Final Boss. Except not only does this lock you out of seeing Zero in the ending, but nowhere else in the game can Zero enter boss/mini-boss rooms — aside from a single necessary case in the intro stage. And there's no indication for him being able to enter this one in particular, either.
Plus the game does a good job of making you never want to use Zero because you need him alive for the best ending, but he dies forever if you ever lose as him at all. Why would you enter the room of a miniboss you've never fought, near the end of a game, as a character who dies forever if you lose as him?
Mega Man Zero 4 had a particularly bad one in the form of the item recipes. You combine two, three, or four chips you get from enemies, and sometimes, you get a special chip that can be used to power up Zero's abilities or give him new ones. Unfortunately, there are a lot of chips in the game, and the only indication you have of whether a particular set will actually make anything is if it does after you put them all together (and use them up in the process). You can get a few recipes from NPCs, and the Cyber-elf gives you (vague) hints about a few of them, but there are far more recipes in the game that you have absolutely no clues for than ones you do...including some quite useful ones, such as the double-jump chip. If you're going for a complete set, hope you like lots and lots of trial and error and farming! Oh, and at least one of the chips you need shows up in only one stage that cannot be revisited and that you are immediately thrust into at a certain point in the game.
In Eversion, you'll have to everse from certain points between different dimensions to succeed. However, eversion points aren't visible, except the background slightly changes and other music can be heard. That caused many players to get stuck on world 2 for a while.
It gets worse in world 8, where many players usually try to take the hardest route.
The Steam release has since made things easier since pressing the "Everse" key will reveal nearby eversion points.
Lampshaded in Donkey Kong Country 3. One NPC will periodically give you hints as to the location of the game's Lost World. If you solve the riddle before he gives you any hints, however, he accuses you of using the player's guide (which is where he got his information in the first place).
Getting the Last Lousy Point for 102% completion in Donkey Kong Country 2. Made much worse when you actually play with a list of every bonus game and DK coin's location, because the last percent comes from visiting the non-level buildings at least once (This includes Swanky, Cranky, Funky, and Wrinkly — the former two don't serve anything useful so a normal player is likely to gloss over them on a second playthrough). Most people tear their hair out trying to speedrun 102% completion because their level-by-level guides turn out to only get them 101%.
...and it goes all the way back to the original DKC. To get 101% completion, you must first access a well-hidden bonus room in Kremkroc Industries, beat a Bonus Round in the level "Oil Drum Alley" in a specific order (get three single bananas, which is considered the worst bonus combination in the game), which will then give you a barrel. You then have to break open the right wall to unlock a bonus room within a bonus room. Your only hint is an arrow sign on said wall. Besides this, many bonus rounds in the first game are found by taking leaps of faith into bottomless pits, or carrying a barrel and running into every wall in each level in the hopes of finding secret openings.
The big clue to the presence of leaps of faith is bananas that seem impossible to collect. Every banana can in fact be collected, so if it seems there is no way, there MUST be a leap of faith allowing for it's collection.
The GBA version makes it better AND worse at the same time. Breakable walls can now be distinguished from regular walls in this port, so if you have an eye for detail you might catch the wall. However, when you get the barrel, you better jump and hug the wall with it — if you are standing on the ground after the barrel is broken, the victory animation will play and you won't be able to go to the secret room. If you jump into the wall though, you'll land on the entry and will be able to proceed as usual.
The infamous hidden stars in Braid, one of which specifically has to be obtained by making a star out of two of the puzzle pieces from World 3 and part of a star visible in the window above the puzzle frame in the house. And if you assemble the puzzle before finding this out, you're boned and have to start the game over. The one in World 2-2 requires you to go to a particular spot and just wait nearly 2 hours for a particularly slow-moving platform to get to a spot where you can climb up on it so you can get to the star. And these two are actually the easiest stars to get.
Of course, performing all the tedious, time-consuming steps to acquire the hidden stars unlocks the bad ending. Since 'Braid' is an artsy game about the nature of obsession, this is strangely appropriate.
The Jumpman games had a large number of these. Pretty impressive, considering there were only two games:
The Grand Puzzle levels (levels 7, 15, and 30 in the original game) nearly defined this trope. Each of these three stages would have four bonus bombs/items that were worth 5 times the normal pick-ups. However, going about getting these required a lot of experimentation to achieve. This is made worse as one mistake would likely prevent you from reaching any of the bonuses at all!
Grand Puzzle I would place a ladder piece on your back if you grabbed any of the bombs aside from four specific ones. You are then to place the piece by climbing to the top of the central ladder. Not only are there no hints aside from the ladder piece to allude to this, but should you die while holding a piece(given the bonus bombs position), the bonus bombs instantly become Lost Forever.
Grand Puzzle II was even more difficult to solve, but at least it wasn't an all-or-nothing gamble. The most difficult one to figure out, though, was how to obtain the treasure at the bottom of the level. Every time you got near the treasure, the doors would slam shut in your face. Solution? Collect one of the bombs and make yourself invisible, then using only sound and minor guessing, feel your way down the ladder and walk to the lamp. Oh, and that had better be the very last item you get, otherwise the gates will close and force you to suicide to escape.
Grand Puzzle III pushed obscure to the limit (in a way it fits, since this is the final level). Getting to the bonus bombs is simple enough. All you have to collect all but four bombs, then jump into the square that's been moving around, which teleports you to an alternate version of the level. Sounds easy enough to figure out...Until you factor in the knowledge that this square will kill you if you touch it at any other time! The only hint you are given is that the square turns yellow when you have enough bombs (hope you didn't have a black and white screen to play this on). Even then, if you don't touch the square at the right place in the level, you will fall to your death when the level restructures itself. Oh, but they saved the best tidbit for last. You have ONE life to get these four bombs with, no matter how many you saved to that point. Die at any time (including from that teleport), and you can kiss those bonuses goodbye! Oh yes, there are eight bombs in the alternate stage, with four of them being not just normal bombs, but instant death-traps...Have fun! On the plus side, when you die in the alternate stage, you instantly go to the end of the game.
Level 20 "Figurit" from the original game is one of the largest offenders on this list. Nearly every bomb you collect will change the layout of the stage, from breaking ladders to adding platforms to creating a deadly pitfall. Should you grab any of the bombs out of the correct order, you will either make the stage harder, force the loss of a life due to you now being in an inescapable trap, or even rendering the stage completely Unwinnable. This wasn't so bad if the player chose "Advanced", allowing them to start at level 19. Otherwise...
The sequel, Jumpman Junior, also made a sequel to Figurit on level 5, "Figurit's Revenge". While it was very hard to make the stage impossible, they increased the number of death-traps, making it very likely you'd lose any lives you had stockpiled to traps you wouldn't know existed until triggered.
Level 25, "Mystery Maze", was a level that was completely obscured in darkness. The only way to uncover the area was to move around, which fortunately would remain permanently revealed on that playthrough. The problem that made this hard is that a few of the bombs in that level were often in areas that required leaps of faith to reach...Not that you would know if the bombs were there or not to begin with, as they too were hidden in the shadows. Also, let's add the fact that there are THREE different versions of the level in this game, with it loading a random one each time you play.
Level 9 in the sequel, "Black Out", had the same idea. Fortunately though, there was only the one version.
Anyone who claims to have gotten the full bonus from the eighth level in the sequel ("Spellbound") on their first couple tries AND without a guide is either incredibly lucky or an outright liar. Each of the twelve bombs in this stage puts a letter in the column at the center of the level. When all twelve are collected, you earn points for each letter placed in the correct order. There is no way to tell which bomb has which letter except with prior playthroughs, nor is there any way to tell exactly what you are spelling, likely leaving several players wondering just what the point of this level was.
Ratchet & Clank: Going Commando: Damosel. At one point, the player is on a ledge and has to swing over to a large area, which has four Mook Makers spewing Protopets. Not only do they hit like a tank and have a knockback on Ratchet, but they can actually spawn more Protopets, and have an irritating habit of approaching from the direction the player isn't hosing with high-quality death if one stays still for about a second. The door to the next area will not open, period, until the machines are destroyed. You could swing down there and fight off the Protopets while trying to destroy the machines. Or you could just shoot them with your Vaporizer. In fact, if you're in the right spot, you can even damage two with a single shot.
Milon's Secret Castle on the NES is so cryptic that Nintendo Power Magazine included an article for it in their cheats section (where normally, things like the famous Contra 30 lives code get published)... The title of the article? "Getting Started"! The Angry Video Game Nerd made a video about it.
The Chick Coins, and some of the rarer eggs in Billy Hatcher and the Giant Egg. For example: The "Super Recky" egg requires you to hatch either a particular item (the Booster), or a particular mount (Datch) in a particular level in Blizzard Castle, and then fly to a location which would not be thought of as accessible (the second outer level of the Ice-Machine Castle). Another example would be where you have to jump around a gate, in order to get to a coin. This is never hinted at anywhere, and isn't that likely to be thought about, seeing as (a) gates are generally impassable until opened, and (b) it's in the second stage of the first level, whilst the game is still in Easing into the Adventure mode.
While most of the New Super Mario Bros. games are generally easy, there's always one or two Star Coins per game placed in extremely counterintuitive places that pretty much either require the player to be psychic or use a walkthrough to figure out. Some of the worst ones included:
Any levels with invisible blocks leading to secret areas. The worst one is probably world 5-1 in 2 and its invisible block hidden in a bonus room, which in turn leads to the secret exit and two additional levels.
The second Star Coin of World 1 Tower in New Super Mario Bros. 2, where the coin only appears when a switch pressed in a far lower part of the screen is active. Made worse by the fact an obvious 'reward' in the form of temporary coins is located in the same room as the switch, causing some people not to even bother thinking to climb/fly upwards.
The second Star Coin in 6-5 of New Super Mario Bros. U is hidden above the level; you must swing on a chain and jump into the sky in a place where there is no ceiling, which warps you to a bonus room.
And the second one in 2-4 is one of the aforementioned invisible block secrets. There is absolutely nothing to suggest that there might be an invisible block above that particular sand spout.
The World 4 Ghost House, meanwhile, could be an example of this trope in its entirety. Secret exit? Star Coins? Heck, this is possibly the only level in a New Super Mario Bros. game where the NORMAL exit is hard to find.
In one of the ghost houses in the first game, there's a star coin in a hidden room but you can only get to that room if you stand on a certain block and jump while crouching to hit an invisible block.
Some of the dolls in Wonder Boy, all of which are required to access the true final area, are well-hidden, such as in rocks, decoy enemies, or fires. One requires a certain frog to follow you until it self-destructs.
In Chack N Pop, you can get the Super Heart in each stage by using the Nth bomb to destroy more than one Monsta. Here N is a function of the number of the stage, and the formula for this function is not entirely obvious.
The iOS game Vector involves the Player Character running away on rooftops from the Thought Police in A Brave New World-like setting. The player must swipe at proper moments in order to avoid obstacles in Le Parkour fashion and collect bonuses for maximum points. Unfortunately, the game is very fast-paced and gets faster and more difficult in subsequent levels. Much information in later levels necessary for the right swipe can only be obtained by having already tried to reach it (i.e. there's no way to figure it out from the information on-screen). For example, certain locations feature "accelerate" moves, usually ending with a long jump. But there may be a wall in the way if you end up jumping. You won't see that wall until you actually try to jump.
The Sega Genesis version of X-Men had a very devious example of this. In the second to last stage, Mojo's Future Crunch, you're meant to hunt down and destroy a console panel at the end of the stage. However, when you do so, nothing happens. What makes this worse is that you're on a time limit, so either you sit there and die or you decide that the game is broken and shut off the game. What no one tells you is that you have to soft reset the game. That's right, you have to lightly hit the reset button and continue on! To make matters worse, you can accidentally reset the game for real if you hold the reset button too long, and on at least one version of the Genesis console (the Nomad, a portable Genesis unit) the level is Unwinnable by Mistake due to the Nomad having no reset button.
Metroid: Other M does this too. The game makes a point of notifying you when your upgrades are authorized, and trying to use chargeables before that time - even to save your life - just causes the charge meter to rubberband. A late boss fight requires you to deduce that you can now use one of them, or die in five seconds if you don't. The problem is that the notification that the item is available for use doesn't come until after the ending credits!
In Cave Story, Professor Booster gets teleported into the Labyrinth by Misery. When the player reaches a certain area, Professor Booster appears in midair and falls a dozen feet, resulting in broken glasses and apparent injury. Getting the good ending hinges entirely on not talking to him. If you try to help him, he gives you the Booster v0.8 and dies. However, if you leave him to his (apparent) death, a Tow Rope will appear in the Core Room, allowing you to pick up Curly Brace after the battle with the Core and save her life; later on in the game, Professor Booster will inexplicably teleport back into Arthur's House in perfect health *and* with fixed glasses and hand you the Booster v2.0. From this, it can be inferred that talking to Professor Booster kills him, and somehow causes a piece of rope found at the bottom of a room several stages away to disappear. The only clues given for this puzzle are a note found in a prefab shack right before the final boss, and a broken teleporter underneath the area Professor Booster falls in with the description "a sufficiently skilled electrician might be able to fix this". The former tells of how Professor Booster is working on a jetpack called the Booster, which is currently in version 0.8, but will be in version 2.0 once he finishes it. Of course, by the time you get to this, Professor Booster has either already died or survived and given you the finished Booster 2.0. The latter obviously explains how Professor Booster was able to teleport to Arthur's house, but the pit Professor Booster falls into is so deep that it can only be escaped with the Booster v0.8 he gives you when you talk to him. Therefore, even investigating what happens to him resigns you to the standard ending. The only way to avoid this is to either have the Machine Gun on you and to have it leveled up to 3, at which point it propels you into the air when fired downwards, or make the pixel-perfect jump from the one tiny red spot before the chasm. Altogether, this all makes getting the good ending (or even knowing of its existence) without consulting a wiki nigh impossible except by accident.
In BattleBlock Theater, if you get into the air through any means other than jumping, you can jump twice in midair. Touching water usually kills you instantly but if you touch it while on fire, it'll launch you instead. If you jump while pushing a block & let go in midair, the block will stay in midair. The game requires you to do all of these things but never tells you about any of 'em.
When you're running the 100M Splash in The Aquatic Games (at least the Sega version), you have to press the A and B buttons in rapid succession in order to move. It is very difficult to hold the controller steady while doing this, but it's possible to work up a good speed. In order to get a medal, you can either spend countless hours trying to actually run the whole race in under 17 seconds and always just miss it (meanwhile rendering your hands unable to grip anything ever again) or...do absolutely nothing for something like a full minute while the penguin kicks you ever closer to the water's edge. The very second you hit the water, start running. The timer resets and you pass the Frog (who left a minute ago in a 17-second race) almost immediately. Duh.
In the introductory cutscene to Castle of Illusion, Mickey makes quick work of three guards by jumping on them. Then when you try it yourself, Mickey gets hurt because you need to press the jump button again to take out an enemy.