The original game (previously titled Final Fantasy Adventure) had an extremely bad case. You are given the following clue from a man in town as a way to the next dungeon: "Palm Trees... and 8." Most players will quickly find the screen with 8 palm trees and begin combing it for the dungeon entrance. The solution? On another screen, you walk in a figure eight around two palm trees. Not even one time; it takes 2 or 3 tracings to unlock the dungeon entrance. While the German translation does give a slightly better hint ("follow the eight at the palm trees"), it's still an obtuse solution.
Trials of Mana
Right in the beginning of the game, the player has to sleep in Astoria's inn to trigger a light waking up the player characters and leading to the next story step. The only hint in the game is a villager saying he's seen a strange light last night, which may return the next night — something that can be easily overlooked as NPCs in this game, and indeed the entire genre, love to bombard the player with useless trivia. The game also has a day/night cycle, so the player might get the idea of waiting until nightfall, only to get... nothing. In any case, if they have no reason to sleep in the inn, they may wander around aimlessly forever, trying to find a hidden way, until either giving up or consulting a guide. On top of that, there's an easily reached Healing Spring near Astoria, so players will be less inclined to sleep at the inn to regain health as there's a source of free healing nearby.
To add to the trickery, the player's goal is to reach Wendel, which is protected by a magical shield. Nothing at all hints at any way to bypass this shield, least of all finding it in a backwater town like Astoria. Instead, between Wendel and Astoria, there's another path with a golden mana statue leading to a dead end. Statues like that are usually placed at important points like boss fights, so the player may take this as an extra hint and run around forever in that forest, with no hope to actually progress any further - until they give up or consult a guide. The remake thankfully fixes this with a waypoint system that will point to where to trigger the next story step.
As balance is almost nonexistent, there are certain characters synergizing extremely well with each other, making the game a piece of cake, while other compositions make it nearly unbeatable. As a player, you have no way to know, and will end up having luck by having picked a good group, or suffer through the rest of the game with an extremely lackluster one. The same goes for classes: you can rank up twice to a higher class, each time having the choice between two higher classes. These aren't comparable or balanced at all, and there is always a best and a worst one. You as the player get absolutely no hints or clues at the classes' capabilities, and will likely end up picking the class that sounds cooler. Probably the scariest thing for the player to do in this game is thus make the mistake of creating a party without a single healer, which is actually rather easy to do; Charlotte's the only healer who will always have healing options. If you don't pick her, you have to pick Duran or Kevin, and you have to choose their 'light' class first. If neither condition is met, you get what many fans dub the 'suicide team,' so named because most of the endgame bosses for any of the paths can do ridiculous amounts of damage that stress your healing item reserves to their limits. Oh, and the party doesn't have Riesz to buff or Hawkeye to debuff, either? Good luck.
The class composition issue also goes story-wise. Every two characters out of the six available ones have a shared background (mostly A's nation attacking B's), they share their ultimate enemies and their final bosses. Only picking two fitting characters for your group will actually reveal the most dialogue for the main character, but you have no way of knowing that during creation.
Legend of Mana
Obtaining the best weapon that can be obtained without crafting (which is itself a Guide Dang It!) requires you to have a save file of SaGa Frontier 2 (another Square game), go to a save point, highlight the save file in the list, and then go to a particular location (whose purpose at this point is solely to get some fairly crappy pets) and fight a fairly difficult boss fight. The "highlight a save file from another game" mechanic? Never referenced anywhere, despite the fact that it is also used to obtain a particular pet early in the game, using a Final Fantasy VIII save file.
The exceptionally deep crafting system and pet raising is so obtuse as to be maddening for the average player (for reference, this sprawling guide might make your head explode just for grasping the basics).
The game is a collection of 67 sidequests. Some of these quests are dependent on the placement of artifacts on a carefully selected piece of the map, with a specific order, and the quests have to be done in the correct order. Some quests require that another quest is not completed or active. In other words, if you want to be able to do all 67 quests in one run, you're going to need a guide. It's next to impossible for a gamer to figure out a structure for the game without prior experience playing it and a lot of mathematics and brain wracking.
Possibly the worst example of this is the quest "Rachel". It seems impossible to find a guide that knew for certain what the requirements for triggering this quest are.
Even figuring out how to complete some of the quests can be extremely frustrating without a walkthrough. Two of the three main story arcs don't make it clear how to start a fair number of the component quests, and to advance in some of the optional quests you have to do things like enter a town area from a specific direction, go to a completely random different town to find a NPC you're looking for (who isn't generally known to be there), and repeatedly talking to the leader of a tribe of creatures who speak a one-word language until a nearby NPC happens to wander close enough that he'll offer to translate.