Gameplay-Guided Amnesia

On TV, writers love clueless protagonists. They're an easy means to provide blatant exposition. Since they haven't the faintest idea of what's going on, in explaining things to them, the writer simultaneously explains things to the viewer.

Video games work much the same way. However, video games developers are faced with a problem. Giving the player a tutorial or providing them with exposition often entails providing the Player Character with information he already knows. To get around this, developers will sometimes strike the player character with amnesia or memory loss. However, more often that not there will be no reasonable explanation for it. Expect lines such as "I shouldn't have to tell you this, but..." or "And just as a reminder..."

It can also result in a character being Overrated and Underleveled, if they're built up as being powerful and experienced but are really no stronger than any other player character.

Common in RPGs, although it's becoming a Discredited Trope these days.

Contrast Justified Tutorial. Also see Selective Memory, Tell Me Again, As You Know. For a more permanent version, see Amnesiac Hero.

Action-Adventure Games

 * In The Legend of Zelda Twilight Princess, Link teaches the village children how to use a sword and slingshot as an excuse for teaching the player. The children seem to already know however, as they seem end up teaching Link.

Adventure Games

 * The tutorial in Phoenix Wright: Ace Attorney consists entirely of an NPC giving the player (controlling the titular, fully qualified attorney) a walkthrough of the legal system of the gameworld. In the first sequel, Phoenix Wright: Ace Attorney: Justice For All, though, the same procedure was justified with Phoenix suffering from amnesia due to injury.
 * In the first game, it's his very first time actually defending instead of merely observing or studying proceedings. And the secodn game has, well, an Easy Amnesia plot.
 * And in the third game, Trials and Tribulations, your first case has the aforemented NPC being told the legal system by her mentor. Even though it's her second trial.
 * And even though everyone was perfectly content to let her go tutorial-less in her first trial, which you get to play later.
 * This one's Handwaved - apparently said NPC stayed up all night watching court procedure videos before the first trial. Presumably, no such videos were watched in the second one.
 * And to be fair, she probably spent a lot of time preparing for her first case whereas her second case was a full year later, and she'd taken the case on only the night before. She hadn't even read all the relevant files.
 * Even though the fourth game opens with another rookie, it finally averts the trope by assuming Apollo knows how the system works but at the same time simply asks if he wants to go over a refresher of the basics before getting into the first cross-examination.
 * Similar to the Trials and Tribulations example, Miles Edgeworth: Ace Attorney Investigations has the 3rd case being Edgeworth's first time doing an investigation, but it's the first case in the game that acts as a tutorial. Just like in Apollo Justice, you can have the basics explained to you if you want and if you choose to do so, it is Edgeworth himself who explains the basics. It is justified since he tells Gumeshoe how he does his investigations.

Beat Em Ups

 * Buffy the Vampire Slayer for the Xbox. By season three, when the game happened, she's already an accomplished Slayer. The training level happens as part of yet another training test done by the Watcher's Council. Which makes sense in context, as the Council is canonically known for not being in touch with reality.
 * And said level is All Just a Dream, too, so you could liken it to Buffy flashing back to an early session with Giles.

Driving Games

 * Justified in the original Driver, in which the main character must pull off a series of driving moves in a parking garage before the criminals will hire him.
 * Though you never actually need to use your newly mastered fancy parking skills in a game concerned with running from the cops across an entire city.

Platformers

 * Mega Man Zero has Zero wake up with almost no memory of his past. Since he's been asleep for 100 years, this doesn't make much difference to the plot -- the real point is to explain why the "legendary hero" has skill level 1 with his own sword. (It also conveniently allows the X games to continue without affecting what Zero should remember later on.) Zero 2 and 3 get better mileage out of the amnesia by "revealing" things that Zero was actually around for in the past.
 * Justified in that Zero in the Mega Man Zero series is not the same Zero from the X series. Its revealed that Zero is actually a copy that inherited the spirit of the non-psychopathic original.
 * Actually he is the original AI, it's just that he's not in his original body.

Role-Playing Games

 * Averted in Fallout. The PC may have to ask about things that are glaringly obvious to the player, like what a farmer is doing.
 * This will depend on the player character's stats, though. A player with high intelligence and the right skills can tell right off the bat what the farmer is doing, and suggest him ways to get a higher crops yield from his fields.
 * Fallout: New Vegas justifies it with a bullet to the head in the opening. On beginning play, the reviving doctor tests the PC on various cognitive and motor functions.
 * In Final Fantasy X, Tidus, an all-star blitzball player, is told the basic rules of blitzball.
 * More specifically, Tidus is in the room wherein other people are reminded of the rules. Other blitzball players - although it could explain their poor record if they forget the rules so often.
 * Because real-world sports players never need rule refreshers.
 * Afterwards he's seen lying on a bench and yawning, so it's sort of Lampshaded in a way.
 * Final Fantasy VII managed to reverse the trope; the tutorials feature Cloud explaining the game mechanics to NPCs, rather than vice-versa.
 * Spin-off game Crisis Core walks headlong into it, however, with 2nd Class SOLDIER Zack needing his friend Kunsel to teach him how to perform basic functions such as taking on missions. In a hidden cutscene Kunsel finally comments on how strange it is that a person who knows absolutely nothing about his job could hold the second-highest rank in the organization.
 * Zack at least doesn't seem like the type of person to remember the specifics and minutiae.
 * Planescape: Torment has you literally starting off as an amnesiac, Waking Up At the Morgue with no memory of who or where you are.
 * Probably due to this trope's ubiquity, and since this was the case in the first Knights of the Old Republic game, some reviewers assumed that starting with amnesia would also be the case for the sequel. This prompted lead designer Chris Avellone to explicitly debunk the claim on the official forums, along with an admission that he "doesn't get how this keeps popping up."
 * In the first game, too, we're not talking the protagonist not remembering anything like in Planescape: Torment, and there's actually little exposition that would require anything more than the situation that you see. At the very beginning, you can ask what the name of the ship you're on refers to, but even the exposition NPC will think that very odd.
 * Final Fantasy VIII frames the tutorials mostly as Quistis, as a SeeD instructor, explaining the game mechanics to Squall, her student. Of course, since the game opens on the day of Squall's final exam, he should really know all of this stuff already. It becomes particularly Egregious when she tells him, at the beginning of the first battle, how to use his weapon. And then shortly thereafter asks if he remembers how.
 * In a disturbing justification, it's revealed that the mechanics of magic in the game often result in massive memory loss. One could assume that "You do know that, right?" type questions are a common means of detection for when this happens. Of course, Quistis is just as surprised to learn about the memory problem as everyone else...
 * She probably just forgot.
 * Mass Effect 2 tries to kind of avoid the trope, so instead of having lost all memories, Shepard gets killed within the first three minutes and then spends the next two years in a secret lab in which the body and brain are restored to their original status. While all memories are restored, you're still back at Level 1.
 * Which makes sense, because you essentially got a whole new body and have been dead/in a coma for two years.
 * At the beginning of The World Ends With You, Neku has to be taught the rules of the Reaper's Game by Shiki. This is later justified when it's revealed that
 * An odd variation occurs in Romancing SaGa: Minstrel Song: the character Darque has Identity Amnesia; if recruited, he has a subplot where he slowly regains his memories. However, which memories he regains are based on which stats he develops -- and with each memory regained, he also gains a free level in one of two different classes.
 * Geralt begins The Witcher with amnesia after an attack, and the implication that he's Back From the Dead. This justifies exposition and eliminates the need for Geralt to know as much about himself as fans of the novels do.
 * Especially good since the game was out in English before the novels were.
 * Every Rune Factory protagonist so far has begun with a case of amnesia (though the next supposedly won't). Word of God has it that there is no deep meaning to this other than gameplay convenience.
 * Strangely played in Riviera: The Promised Land, Ein, the hero Grim Angel is needed to be told how to fight. This can be quite justified since it's his first battle, but even though he get knocked out and lose his memory later on, he doesn't need any tutorial to help him reminding how to fight or use a Limit Break.

Stealth-Based Games

 * Part of the reason for the main character switch in Metal Gear Solid 2: Sons of Liberty. There's only so many ways you can write "I shouldn't have to tell you this, of course."
 * Considering the fact that the main character is highly trained, if not necessarily experienced, they still had to figure out a new way to write that. And then, lampshaded at one point, when Raiden says, "I've completed over 300 missions in VR. I feel like some sort of legendary mercenary," to which Campbell replies "...okay, we'll skip that part."
 * In all the other Metal Gear games (including the Tanker chapter of 2, where you control Snake), someone explains the controls to Snake. Apparently he needs Otacon to tell him how to fire a gun.

Third-Person Shooter

 * In Psi-Ops: The Mindgate Conspiracy, protagonist Nick Scryer takes an amnesia-inducing drug in order to infiltrate a terrorist organization, and gradually remembers how to use his many powers as the game progresses.

Turn-Based Strategy

 * The first few chapters of Advance Wars 2 and Dual Strike serves the function of the Justified Tutorial found in Advance Wars 1. To provide variety, the character 'teaching' and the character being 'taught' varies from level to level.
 * Though this can make seasoned commanders seem like idiots. Justified with a few of the characters like Max (hot-headed and doesn't rely on subtelty) and Andy (The Ditz).
 * The the protagonist of the first Disgaea game is out of shape after sleeping for 2 years, has lost all his power, and requires a recap on the basics of combat.
 * In Agarest Senki 2, after Weiss gets flung out of the gods territory, he gets a Laser-Guided Amnesia and thus forgets his skills. He then gets a tutorial from Aina and from the others.

Wide Open Sandbox

 * S.T.A.L.K.E.R. uses this one to its full extent. It looks like the amnesia is merely gameplay guided. When the character finds out, the justification is more like The Reveal.