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 Mega Man 7, the locations of every important item you can get with Rush Search can qualify. But the Energy Equalizer takes the cake. While the rest of the items can be found by just using Rush Search on every different ladder, to get the Energy Equalizer you need to defeat the Shade Man miniboss in a specific way (by attacking the outer shell). There's no indication to make it appear you're making any damage other than the eyes of the pumpkin flashing. Once you defeat it, without touching the inner core, the boss will explode on the right side of the screen revealing an entire new section for the level. Once there you will need to scan the entire new section to find the Energy Equalizer... or you can use Rush Search under the Dr. Wily portrait to find it.
Getting the Proto Shield is even worse. First you need to find Proto Man in Cloud Man's stage. No big deal, just use Rush Coil to get to the suspicious stair you otherwise can't reach. Proto Man will give you an entirely redundant and irrelevant hint (Use the flame weapon in the woods). Nice, I guess? Except you don't have a flame weapon... yet. Until this point, you could think it's the same as Mega Man 6 where Proto Man only gets a cameo to give you the Energy Equalizer except this time he didn't give you crap. Here comes the guide dang it part: You need to find Proto Man again on Turbo Man's stage. To find him you need to go through a fake wall at the top of the Hyper Rocket Buster room. This time, there's absolutely no indication of the fake wall's existence so you kinda need to stumble there. Once again, he gives you a totally irrelevant tip (you can't slide while using the Super Adapter, something you can easily know as soon as you get the Adapter). And you're not done yet. Now you need to go back to Shade Man's stage. Once you destroy the pumpkin mini-boss the normal way, you will get to a room with a lone Sniper Joe. You kill him and then you proceed through another fake wall to a new room where you will finally fight against Proto Man, and once you defeat him you get the Proto Shield. And unlike the Energy Equalizer and the other items in the game, you can't buy it at Auto's store. All of this for a quite mediocre reward that gimps your offensive skills.
In Mega Man 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).
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 permanently lost 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 unobtainable 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 specific mini-boss fight in one of the final levels (when you normally can't bring him into boss fights at all) and then let it hit him with its Last Ditch Move. This damages Zero, making him unavailable for the rest of the game just as if he had died, but unlike dying anywhere else in the game, this one arbitrary time he'll make sure to talk to X and hand over the Z-Saber first.
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.
Mega Man ZX missions require you to travel to the location where the mission takes place, unlike other Mega Man games where you're just teleported there. Unfortunately, you don't get good hints as to where these areas are, making it very easy to get lost in the Metroidvania world. ZX Advent recertifies this with a more accurate mini-map that shows where you need to go even if you haven't actually explored that area yet in order to show you're on the right track.
Prince of Persia
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...
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 unobtainable.
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.
After finishing the level, one might notice that four of the bombs produce a space, a J, an X and a Y. It takes just a little anagramming to figure out the phrase is "EPYX JUMPMAN". Of course, now the trick is realizing you have to spell it backward.
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 order to get to Rusty Bucket Bay, 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.
Speaking of Rusty Bucket Bay, you never get a clue that you can actually break some of the windows of the ship, or that there's a hole in a wall underwater in Snacker's pool leading to a warehouse with an empty honeycomb piece. The only slight hint for the windows is that some of them reflect light differently than the others, and these are the breakable ones.
There's also the pink Jinjo in Rusty Bucket Bay, who is found deep underwater underneath a grate. Considering how the polluted water functions in Rusty Bucket Bay, many people tend to avoid the water as much as possible.
How to get the colored mystery eggs and the ice key. Yes, they're in there. Yes, you can do it. But how? The whole point was this trope: You weren't supposed to know unless you'd managed to get clues from the next game. When Nintendo stepped in and changed the hardware, implicitly telling Rare they couldn't do it the way they wanted (it's a long story), this idea was scrapped as far as the sequel went... but it didn't change what was already put into the first game. Not that these items actually do anything,note Not only would the next game tell you how to find them, it would also be the only place you could use any of them but it's still been one of the longest-standing brainteasers in gaming history.
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 A.I., 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. Although somepeople have managed to beat her through sheer mashing on the last race. 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.
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: The train station isn't next to the aforementioned switch.
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.
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.
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.
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.
In Cave Story, there is a small room in the labyrinth with a wide gap between the entrance and exit. When the player enters, Professor Booster is suddenly teleported into the room in midair and falls offscreen. If you go down to talk to him, he gives you the the Booster v0.8, a jetpack that allows you to easily reach the next room, and dies. However, getting the good ending hinges entirely on not talking to him, and instead making the difficult jump across the gap on the first try; if you fall, you can't get back up without the Booster (unless you happen to have gotten and fully leveled the Machine Gun). This is made somewhat easier by a subtle mark on the ground at the spot you have to jump from, but it's easy to miss. If you make the jump and leave the professor 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 (although several more steps are required for a full recovery); later on in the game, Professor Booster somehow appears in perfect health at Arthur's House, where he hands you the Booster v2.0. It turns out that the professor, having 'not given you the Booster yet, finds the strength to make it to the broken teleporter at the bottom of the room, repair it, escape, make a full recovery, and finish work on a much more powerful version of the Booster. The only clues given for this puzzle are a note found in a prefab shack right before the final boss, and inspecting the broken teleporter to learn "a sufficiently skilled electrician might be able to fix this". How this causes a piece of rope found at the bottom of a room several stages away to disappear is not explained, but this saves the player the trouble of going through the rest of the steps to reach the true final area only to find it nearly impossible without the Booster v2.0, and makes it slightly more obvious that something was missed. Altogether, this all makes getting the good ending (or even knowing of its existence) without consulting a wiki nigh impossible except by accident.
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.
Crash Bandicoot (1996) had The Great Gate and Native Fortress, which had boxes hidden in that background that could be accessed by jumping behind the wooden wall at some points, so you could No Death Run the entire level only to find you missed some of these boxes (in particular since these levels don't keep a track of them). Others levels required Leap of Faith on invisible bridges. Some of the levels needed to get colored gems from other levels too, with no indication of which level contains which type of gems. Also, the Final Boss shoots you with differently colored shots, one type of which can be spun back to him, but game doesn't tell you this.
Crash Bandicoot 2 had some secret parts in levels which included jumping into a Bottomless Pit that doesn't look any different except for three wooden planks which get destroyed once you emerge from the level on a floating platform. Jumping through a fake wall where the only hint of a clue to it is why there are so many Nitro crates leading up to a supposed dead end. Or ascending a Nitro staircase which doesn't look any suspicious except the boxes don't bounce. There were some secret entrances to certain levels, which had to be accessed by feats like bodyslamming a certain enemy on a platform or jumping across crates floating in water to reach an isolated platform.
The Third game had it worse for one of its truly secret levels, where you had to run into an enemy to get transported to it. A less subtle, Crash 2-esque secret entrance in the game is accessed by knocking down a peculiar road sign in a motorbike level.
Lampshaded in Donkey Kong Country 3: Dixie Kong's Double Trouble!. 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: Diddy's Kong Quest. 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 Donkey Kong Country. 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 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.
Donkey Kong Country: Tropical Freeze has the series-wide roll jump ability, where if you roll off a ledge, you can jump in midair. In the other DKC games, this move was explained in either the manual or the game itself, but Tropical Freeze doesn't touch on it in either location.
Dr. Chaos suffers from this big time. At the start of the game you're plopped into a side-scrolling segment in a house with doors that take you to point-and-click room exploration sections. You can find items, fight enemies, battle a few mini-bosses if you happen to unleash them, and... after about 5 minutes you've gone everywhere you can go. This is the point where 99% of people put the game down and never played again. You're just expected to know that one specific cupboard in one specific room, unlike every other cupboard in the entire game at this point, is a portal that can be entered like a door and it warps you to the next level. Once you beat this next level you find a MacGuffin which not only unlocks all the other hidden portals in the game but flashes when you're in a room with one, and the game actually gets a lot more straightforward, which, sadly, probably prevented the game from becoming fairly popular: once you know what to do it's an honestly decent game with strong Metroidvania elements from before that was even a genre, but because of this incredibly obtuse element at the very beginning very few people got far enough into the game to find the diamond in the rough.
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 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.
Frogger Ancient Shadow has four health upgrades to extend Frogger's health from four hit points to eight, but while the first three are simply bought from Mohan's shop, the fourth one is found in a completely unrelated location so obtuse that without a guide, you may simply settle for having an incomplete seven health. It only becomes accessible after beating the boss of Doom's Temple, the penultimate world, when Frogger decides to "go home and see my friends". In order to access it, you need to talk to Lily, decline her request to hang out with Frogger, and then go to where you would meet her anyway. As to where that is, the only hint is that if you agree to hang out with Lily, she tells you she'll be waiting in "the regular spot", which is the Practice level by Frogger's house on the world map. Once you go there after turning down Lily, a cutscene plays where Frogger meets Berry (who in the main story of this game has only appeared as a voice narrating her letters to Frogger) and receives the final health upgrade from her (for reference, Lily gives you a revival potion).
Finding the rainbow drops in Kirby's Dream Land 2 might not be so bad, since you're just supposed to find one per world: just sifting through each level will eventually lead a player to find them. Unless you're looking for the one in Cloudy Park, which requires using all three animal friends (and only Rick and Coo are found in the stage, meaning you need to bring Kine in from a different level to even begin the search) and going back and forth between rooms constantly switching copy abilities.
In Kirby's Dream Land 3, you need to find a heart star in every stage of every world to reassemble the Rod of Love and access the true final boss and ending. While some are rather straightforward (such as finding a secret area, avoid stepping on certain flowers who will look sullen if you touch them, finish a stage with a certain animal friend or beat a mini-game at the end of the level), some are way more cryptic (such as having Chuchu at the end of the level and using her normal attack on a certain NPC) and a few even counterintuitive (in another level you instead have to do step on flowers which are identical to the ones you have to instead avoid in another level). The ones that are absolute hell to do without a guide and still tricky with one are Levels 2-5 and 3-6.
2-5 is apparently simple, since in the final screen there is a pink bird which suggests you need to clear the level with Pitch. However, midway through the level there is a screen which is impossible to get through unless you take Kine from a nearby room. Finding Pitch in this level requires finding two different copy abilities in out-of-the-way rooms to break through a certain wall.
In 3-6, meanwhile, you need to scour a dungeon (which has points of no return) for all the pieces of R.O.B.. To access the rooms where said pieces are located, you also need to use Kine and Coo, which maneuver awkwardly to say the least in the cramped spaces, including using a secondary ability of Kine with the Spark ability (revealing invisible elements to identify the correct door to enter) which is never hinted at and not used in any other stage in the game.
Many nuances of how certain elemental abilities affect bosses may get overlooked (or never discovered) even after finishing the game. Some, such as putting out Flamberge's cannon's fuse with Ice, Wind or Water or instantly killing Whispy Woods by dealing uninterrupted Fire damage are pretty obvious and might even be done by accident, but would you expect that using the Ice ability on Kracko's rain attack for several seconds would freeze him entirely, especially since for the first few seconds he doesn't even take damage from it? Or that using a Fire ability on Francisca's icicles will net you healing items, and using Spark on her water stream will damage and eventually stun her? Even though the story mode's bosses are rather easy, these strategies are invaluable in the Ultimate Choice at higher difficulties or to speedrun Guest Star mode.
One thing many will never find out on their own unless they randomly dick around is that King Dedede and Meta Knight can be added to your party immediately after defeating them by throwing a Friend Heart in a brief window of opportunity (just after he shrinks back from his Buff self for Dedede, after he lands but before his mask breaks for MK). The small heart symbol that shows they can be recruited does appear on their head...but only if you're currently in the act of throwing a Friend Heart, which you wouldn't be doing randomly unless you already knew about it.
To beat Scar in The Lion King game you need to throw him off the cliff. Nothing in the fight itself specifies this, so anyone who played the game before seeing the movie will likely be stumped.
Getting all Emblems in Luminous Avenger iX is simple enough if you just thoroughly scour every stage... except for one specific Emblem that 99% of the players will only find by accident without looking it up. It's in Data Center Beta. To get it, you have to have Anchor Nexus active in a specific corner at a dead end to reveal an invisible enemy that's drops it when destroyed. There is the only Emblem in the entire game that drops from an enemy and nowhere in the game do you ever use Anchor Nexus to reveal invisible enemies.
Metroid: Other M 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!
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 main difficulty comes from the existence of blocks that need to be pushed, allowing you to proceed further... but even if you find these blocks, it's very hard to even figure out that Milon can push blocks, since it's not mentioned in the manual, he lacks a "pushing" animation, and even if you do stumble into one by mistake, it takes about a full second of Milon running into it for it to start moving. There's also a lot of "puzzles" that require you to shoot empty air.
Mischief Makers... hoo boy, was THIS one cryptic. Not essential to the game but necessary if you wanted the secret full ending were the gold gems. Some were easy to get, some were hard to get but at least you knew what to do, and others...
Some NPCs hold gems that can only be acquired by shaking them. From that, you would infer that the only possible way the gold gem can be hidden in "Clance War II" is that it's on somebody you need to pick up & shake, since there are no background objects whatsoever to interact with, but try finding which of the dozens upon dozens of guys is holding it without a game guide. Some of them get blown up, sometimes blowing themselves up, before you can get anywhere near them, making searching every single enemy in this level impossible.
The Steam version of Psychonauts has achievements for unlocking cutscenes that are very easy to miss unless you know where to go and when.
In Pac In Time on the Super Nintendo, there's a section in level 22 where you have to open a lid on a pipe in order to drain the water from an adjacent room to reach the exit. However, nothing you use seems to work on it. What you have to do is slowly approach the pipe, (It has to be slowly, otherwise you bounce over it.) which causes Pac Man to start pushing against it, then use the rope, which was only used up to this point to grapple from the ceiling, and pull the lid off. This is at least 2 hours into the game, and the rope was only used for grappling, so how was the average player supposed to know that it suddenly can be used to pull things now?! The only way you'd know this is if you had the manual, which tells you how to do this, but if you rented the game, you would have no idea that this was even possible!
Most of the franchise has Skill Points, which are this. They're essentially certain actions you need to do like luring an enemy into a force-field or destroying all breakables on given location. In the first game, you don't even have access to the list of these Skill Points' names until New Game+, and even then you have only access to that and which planet Skill Point concerns.
Some Gold Bolts in Ratchet & Clank (2002) can be this. While the late-game Map-o-matic indicates secret areas, good luck if the Gold Bolt is in the main area but well hidden or if the path to it isn't immediately obvious. Next games point them even in those cases by green point once that item is obtained.
Ratchet & Clank: Going Commando has 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.
In Ratchet & Clank: Up Your Arsenal, one of the Titanium Bolts on Metropolis is located on the Galactic Ranger mission subarea, on an unassuming Grav Boot track pointed away from the center of the map. There's a good chance you won't notice it, as you're never required to, or even able to, go over there on foot without glitches, meaning you'll likely only scoop it with a Hovership.
Rayman 2: The Great Escape has a number of collectibles called "Lums" to find, but if you want to find all of them, you'll have to break the rules somewhat. Most of the collectibles are in hard-to-reach places, but they're almost always immediately noticeable as you play the level or explore a little. Unfortunately, in the original versions of the game on the Playstation and Nintendo 64, the very last Lum of the game can only be found by jumping through a solid wall in the "Tomb of the Ancients" level. Nothing else in the game indicates that this is something you can do, and it's only able to be performed in that level. The remake of the game for PS2 eventually gave up on this little-known secret and placed it in a chest you can access at the end of the course.
In the original Shantae, the final dungeon is on top of Mount Pointy, which Sky tells you is to the east. Since this is a 2D side-scroller, logic would dictate that east means right. She also says it's far away, which makes sense since her home town of Oasis Town is as far west as you've explored so far. And technically, she's not wrong, since the game world wraps around and if you do go as far to the right as you can, you'll end up at Mount Pointy... at the edge of an impassible cliff. To get to the dungeon, you actually have to go left from Oasis Town and approach the mountain from the other side. What's worse, if you try to explore further left and hit the slippery slope, you'll fall down the other side and get stuck at the far right edge of the world all over again. Hope you've been stocking up on Warp Squids and had the foresight to save four for Oasis Town!
The Simpsons: Bart vs. the Space Mutants had several non-intuitive aspects throughout the entire game, but by far the worst is the final plutonium rod in the final level. Each level has an object that the titular space mutants want, and Bart has to either destroy, collect, or obscure them to prevent the aliens from succeeding. For the first four levels, there are more items than what are required, so Bart can afford to miss some on the way towards completing the level. On the final level, they're after plutonium rods at the power plant, and there is one less than the required number lying around the level. More than one gamer threw controllers in confusion and disgust before learning the solution - Maggie is using the final rod as a pacifier, and interacting with her after putting the other 15 in place finishes the game. Nothing like this was at all necessary previous in the game, nothing hints that it's even possible, and it also won't work if Bart hasn't put back the other 15 rods first.
Spongebob Squarepants Revenge Of The Flying Dutchman is infamous for its Jellyfishing fetch quest in Jellyfish Fields for this very reason. In order to obtain the Reef Blower, you need to catch 100 Jellyfish. The problem? Jellyfish Fields only has 84 Jellyfish, and the contest doesn't tell you that it takes into account the Jellyfish in other levels. This is combined with the issue that the game GUI only lists the Jellyfish you've caught in the current level you're in, and not the combined total you've caught in other levels beforehandnote The grand total is only listed in the pause screen. As a result, many people become stumped to the point that they end up backtracking and searching Jellyfish Fields for hours just to find the remaining 16, without even knowing that they already have over 100 Jellyfish the whole time. It's such a big issue that YouTuber LambHoot points it out in full detail in his review, twice. The latter of which, even mentioning this trope by name.
Spyro 2: Ripto's Rage! and Spyro: Year of the Dragon have Skill Points, hidden objectives you can complete in various levels that unlock an extra Where Are They Now entry in the Guidebook / Atlas if you collect them all. Unlike every other collectable in the game there is no hint that these are a thing, no entry in the pause menu, and they don't count for 100% Completion, and as they are very esoteric actions (like destroy all the seaweed in Aquaria Towers or burn all the trees in Sunny Villa) most players likely won't even know they're a thing, while players who happen to stumble across them will have no hints at all where to find the rest of them, or how many they've even completed. Even players following a walkthrough will have to keep track of which ones they've completed all on their own as there's no in-game way of knowing if you've completed a Skill Point challenge. The Spyro Reignited Trilogy remakes do have a list of Skill Points accessible from the pause menu, but the descriptions are vague enough to make hunting for them a chore anyway.
Super Pitfall might as well be called Pitfall!: Guide Dang It! as it is this trope in spades. Power-ups only appear when you jump in very specific places which is a complete guessing-game, you must warp by jumping into walls, and at one point you must jump into a bird enemy to warp, which of course looks completely identical to all the other bird enemies in the game which kill you. How anybody could possibly figure out how to beat this game in 1987 before guides on the Internet is anybody's guess.
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.
In Vexx, the second heart of the second world requires you to backtrack to the first world, go halfway through one mission (which requires platforming up a tower), land on a narrow platform and hit a switch, then climb the underside of the bridge to reach the opened door to access a second tower where the mission resides. Nothing in the clue tells you anything about how to get to the mission.
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.
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 Unintentionally Unwinnable due to the Nomad having no reset button.
Yooka-Laylee and the Impossible Lair. There's a secret exit at the end of Gasping Glade, past a seemingly uncrossable pit of goo. No matter how far you jump or which tonics you equip, you'll always miss the ledge by an inch. The solution? Just sit and wait. Eventually, a platform appears automatically to help you cross safely.