A narrator is an entity within a story that drives the story further or explains to the player different aspects of the game. However, the credibility of the unreliable narrator is questionable, due to faulty memory, insidious schemes, bias, physical limitations, or mental instability. This device can be used in different ways:
A narrator commonly found in video games, he serves the purpose of teaching the player the controls and mechanics, and guiding them through an in-game tutorial. By doing so, he touches briefly on the fourth wall, often referring directly to input commands and button combinations that would not otherwise make sense. Although rarely seen over the course of an entire game, this narrator is often used for tutorial missions or as a guide for the player's next course of action. The nature of the narrator's unreliability varies from game to game; some may be evil, purposefully spreading disinformation to the player in the form of tips that result in his death or go nowhere (such as Big Boss in Metal Gear and SHODAN in System Shock).
A character that has a role in the plot of a game and also fulfills the task of narration is known as a character narrator. He may or may not be the main playable character. In Prince of Persia: The Sands of Time, The Prince is relaying previous events by narrating his story to an unnamed individual. The player controls these memories. If the player dies during the game, that means the narrator would be dead, thus creating a paradox. Whenever the player dies, The Prince interjects saying "No, that's not it," explaining the player's actions as an error in his memory. This makes it so the death didn't actually happen and the story resumes. This creates a situation of the The Prince constantly lying to the player and contradicting himself, making him an unreliable narrator. A more extreme example of an unreliable character narrator would be Cloud Strife, the main protagonist of Final Fantasy VII. Cloud gives both the player and his allies a retelling of past events that later turn out to be false and unreliable.
In some instances, an instructional narrator tends to give the player helpful advice early to ensure their success in whatever their given role in the game, but then later reveals himself to be operating as a counter-agent to the player's goals, despite the initial assistance. In some cases, this also happens to be because the given narrator was not who they claimed to be in the first place. This usually results in the player character being left mostly on their own to undo the damage they've caused at the hands of their misinformation, and pursue the narrator, as seen in games like Metal Gear Solid and Bioshock. In these specific instances though, the narrator is only in a narrative role for short stints, instead being presented as a character who explains things. Possibly some of the most infamous deceptive narrators are The Colonel from Kojima's Metal Gear Solid 2: Sons of Liberty and GLaDOS from Valve's Portal.
This kind of narrator offers much more color than commentary and can adopt one or more of the concepts mentioned above. One great example of the compound narrator is a character by the name of Lance Boyle. He is the host for the MegaRace virtual reality TV show made by the VWBT TV network in the game MegaRace. At the beginning of MegaRace, Lance Boyle helps the player out by giving him/her a full breakdown of what one needs to know in order to survive in MegaRace. He is a character narrator in the sense that he was once an "enforcer" or contestant of MegaRace at one time and even alludes to this truth in certain cutscenes within the game. After the tutorial introduction of MegaRace, Lance Boyle does nothing but discourage the player from trying to even play the following level through intimidating and talking the player down. He also criticizes the player for making certain mistakes and even freaks out when the player takes a little too long to select a car before the next level.