Memario

Memario, also known as Replay Mario or just Replay, is an anomalous character that can appear in some personalized copies of Super Mario 64 DS. They appear as some kind of robot variant of Mario with dark red clothes and gray overalls, no face and dark hair. They can reportedly appear in an anomalous area similar to the Rec Room known as the Castle Theatre. They allow the player to rewatch them playing a level, but is also extremely buggy.

Description
Memario can be seen upon entering the Castle Theatre and interacting with one of the objects would allow you to view a mission you have already cleared being played by Memario, even if the character being used was not Mario. Some say that Memario will put on a mask representing the character the player played as in this mission, or simply t-pose due to the lack of animations. Once they collect the Power Star at the end of the mission, the screen will fade back to the Castle Theatre. If you died in the mission being replayed, this will usually result in the same thing as collecting a Power Star but it can also result in the game thinking the player died or crashing the game entirely. Memario may also get lost trying to copy the player's movements, resulting in Memario trying to "play the game itself" as reporters have described it, or just stand still aimlessly, softlocking the game.

The Castle Theatre
The Castle Theatre is the area Memario is most commonly found. It is usually found as an attachment to the Rec Room or appear in the character room as well, unlocked after getting 2-6 Power Stars. The room itself has multiple pieces of recording equipment, chairs, and a projector screen. The walls appear similar to that of the first floor's. If you interact with the projector, or another item depending on the copy, it allows you to view Memario's replay of a mission. It may be completely random, allow you to select a specific mission from a random selection or select a course to get a random mission replay.

Notably, some say that a Lakitu Bro can be seen in the Castle Theatre, likely due to them being the only characters to hold cameras and record the entire game for a movie according to Satellaview. Their dialogue usually explains how the projector screen works, along with some exposition on their purpose in the game. Some have even said that their dialogue changes depending on your progress in the game.

Double Replay
In some instances of only Memario replaying the level, the player will be warped into the level alongside Memario. This usually results in Memario running off screen, allowing the player to run around until Memario collects the Power Star, though the camera may follow after Memario, requiring the player to have to keep up or else lose sight of their character. Alternatively, Memario may act more like a Shadow Clone, racing the player to the Power Star or attempting to hinder the player's progress, usually only if Memario is provoked by the player attacking or interacting with them. If Memario collects the Power Star, the game will usually return to normal or crash. If they die, this will usually softlock the camera but it can also allow the player to obtain the Power Star themselves. If the player beats Memario to the Power Star, the game is more likely to crash, but some say that the Lakitu Bro in the Castle Theatre has congratulated them on beating Memario, implying this is either a planned feature or the Personalization A.I. taking a glitch and making it a feature.

Castle Manifestation
According to some who have encountered Memario, they can randomly appear in the Castle Theatre, replacing the player character until entering a level or another replay which will reset the player character back to normal. However, Memario may appear on their own in the Castle Theatre as an NPC, which the player can interact with. They usually have blank dialogue, notably with the jingle that plays upon interacting with Toads, or some other dialogue from somewhere else in the game, even unfitting text strings or unused text. Memario will then follow around the player, mimicking their movements after a second or so, until they enter a painting, which will usually either leave behind Memario or they will enter the game and replay a mission or slow the game down significantly as the game attempts to load the level twice, one for the player and once for Memario, typically resulting in a game crash.

Theorizing
Memario and the Castle Theatre were likely scrapped to allow for more additions such as minigames, extra levels or due to the inefficiency, as some missions may take too long and be inconvenient and uninteresting to watch. It was likely also hard to code and maintain, indicated by the anomaly's buggy nature. The Double Replay phenomena's competitive Memario is notable as it appears to be the A.I. repurposing a glitch into a feature in a similar manner to the Self-Patching Anomaly.

The presence of the Lakitu Bro is also notable, as it may have been the developers attempting to make the characters more relevant as besides for being the camera that the player views the game through and occasional tutorials the Lakitu Bros. do not serve much of a purpose. Them showing the player their recordings in the form of Memario may have been a way to give them more screentime in Super Mario 64 DS.

Memario's design may have originally been more complex but was simply not finished and what's left is a placeholder created by the A.I. to reimplement the character and mechanic to the best of their ability. Why they do not apply Mario's eye textures is unknown, though it may be to make Memario appear more "robotic" as they are imitating the player.