In Super Mario 64, the courtyard at the back of Princess Peach's Castle includes a statue of a Power Star, where Mario spawns from if he is ejected from the nearby course Big Boo's Haunt. The illegible writing on this statue's plaque became the game's greatest mystery for 24 years, with the interpretation "L is real 2401" prevailing as the most popular reading, and a recognizable way to refer to theories surrounding the statue.
Rumors on how to unlock Luigi included (but were not limited to) collecting every coin in the game, running laps around certain landmarks, and collecting every Power Star under a time limit. On November 13, 1996, having received constant fake strategies for how to unlock Luigi, video game website IGN offered a US$100 reward for an authentic unlock method; the bounty went unclaimed as no proof of Luigi's existence was forthcoming. An official statement from 1998 explains that the plaque is intentionally illegible and meaningless, and no hard evidence to the contrary has emerged.
The texture for the plaque was reused in The Legend of Zelda: Ocarina of Time. The Super Mario 64 statue reappeared, using the original model and textures, in Super Mario Odyssey's reconstruction of the courtyard.
On December 2, 2016, redditor b0nd18t posted an image of a letter they received from Nintendo of America on May 7, 1998. The letter contains the following official explanation of the plaque's inscription.
Many people think that it’s a hint that Luigi is in the game and it has something to do with a special code. The real answer is that the programmers put it in there as a joke. They thought people would try and try to figure out what it means. It doesn’t have any meaning at all.
L is real 2401
The most common interpretation of the plaque's inscription was that the top line reads "L is real 2401". Consequently, the plaque was theorized to have connections to Luigi, a character who makes no appearance in the game.
A popular urban legend was that Luigi could be unlocked as a playable character. Interestingly, multiplayer with Luigi was originally planned for Super Mario 64. The feature was removed before the game's release, along with any trace of Luigi's assets. As technical knowledge of Super Mario 64 has grown, unofficial models of Luigi in the game's style have propagated online.
Players spread rumors related to unlocking Luigi, sometimes involving the perceived number 2401.
One rumor claimed that 2401 represents the total number of coins in Super Mario 64, and that collecting them all and returning to the statue would unlock Luigi. While collecting coins does unlock Power Stars elsewhere in the game, this rumor is false, as the maximum value of unique coins in the game (without duplication glitches) is 2657. This includes a few misplaced coins that are inaccessible without glitches, lending further doubt to theories that assign a meaning to the game's coin total.
Note that a player could obtain an arbitrary coin "total" by using glitches to duplicate coins. If these glitches are counted, it's trivial to claim any "total" of coins whose addends the game can store, such as 2658, 3231 (sum of maximum saved coin scores; each ≤ 255), or 14985 (sum of maximum in-level coin scores; each ≤ 999).
Another rumor claimed that running around the statue, or alternatively the castle grounds, 2401 times would unlock Luigi. This may have been inspired by the method to defeat the Mr. I enemy, which appears in the nearby Big Boo's Haunt. The magnitude of this action made the rumor difficult to disprove, as making thousands of laps is a long process where it's easy to lose count, and the inevitable lack of results could be blamed on an unnoticed mistake anywhere throughout the process.
Around 24 years and 01 month after Super Mario 64 was released, Luigi's unused 3D model and textures were finally discovered. This hints that the statue was a prediction that someone would find the Luigi model after only 24 years and a month, which can explain the number, 2401.
L is real in Paper M
A separate theory around the "L is real" interpretation was that it was hinting at Luigi's later role in Paper Mario, which released in North America on February 5, 2001, one day after 2-4-01. Under this interpretation, the bottom line could be read as "in Paper M", lending the full interpretation "Luigi is real on 2-4-01 in Paper Mario".
However, several factors made this theory unlikely even before this mystery was officially explained.
- Super Mario 64 was released on June 23, 1996. The developers would have needed at least five years of insight to foreshadow the North American 2001 release date of Paper Mario, and even then, the supposed date listed on the plaque is incorrect. Paper Mario released in North America on February 5, 2001, a day later than the "L is real" sources cite.
- North America was not the first region where Paper Mario was released. The process of localizing the game from Japanese to English would have made Paper Mario's eventual release date even harder to predict. In addition, Nintendo is infamous for different regions having different release dates, as well as overall delays while developing their games. There is no likely way the developers made such a close guess for a release date for an unrelated, second-party game in another region.
- Japan uses a different, big-endian date format, yyyy年mm月dd日, as opposed to the Unites States' middle-endian mdyy format suggested by the "2401" interpretation. If the date were rendered this way, it would read "2001年02月04日", or at least "0124". The Japanese release date of August 11, 2000 is "2000年8月11日", which might then be "00811", which is a different length entirely. Either way, momentary adoption of the middle-endian format would come at the expense of other regions entirely. Most of the world uses the little-endian DMY order style, so ten times as many people would have read 2-4-01 as 2 April, 2001. As with imperial units, the USA is one of the only major regions to use middle-endian.
- The plaque was reused before the release of Paper Mario; specifically, in The Legend of Zelda: Ocarina of Time. This game is completely separate from Super Mario 64, apart from using a heavily modified version of the same game engine, and including a few subtle references to the Mario franchise. Either way, in Ocarina of Time, the perceived message on the plaque would be irrelevant, supporting the official statement that the texture has no specific meaning.
Perhaps the greatest blow to this rumor is the fact that Luigi is only a minor character in Paper Mario. Therefore, it would make little sense to foreshadow his appearance there. As a result, some players argue that the statue plaque alludes not to the character himself, but to Luigi's diary in Paper Mario, which then foreshadows Luigi's Mansion in a chain of references. This is already quite unlikely, and could become even more unlikely depending on whether Luigi's diary makes the same reference in the original Japanese script—something for anyone fluent in Japanese to look into!
Consider that Paper Mario and Luigi's Mansion had development cycles that were concurrent for a long time, with the games' initial releases in 2000 and 2001, respectively. Super Mario 64 and Paper Mario did not share as much development time. By proxy, neither did Super Mario 64 and Luigi's Mansion, releasing six years apart; meaning that the former could probably not have made this eventual reference to the latter. The ostensible purpose just to indirectly foreshadow a game starring Luigi, five whole years prior to its release, makes this conundrum even more far-fetched.
Of course, rumor-spreading sources could easily argue against any of the above points. None of them outright debunk the original assumption that the bottom line of the plaque reads "in Paper M". Accordingly, regarding this claim in isolation, several localization details from Paper Mario's own development show that the "in Paper M" inscription would be physically impossible.
First, the title "Paper Mario" was not finalized at the time of Super Mario 64's release. In Japan, the game's final title was never Paper Mario at all. Rather, it is Mario Story, a vastly different name. (Japan did not adopt the Paper Mario name until what English players know as Paper Mario: The Thousand-Year Door, which was originally called Paper Mario RPG.)
This implies that localization staff, who were probably entirely unrelated to the development team of Super Mario 64, were the ones who made the decision to rename the RPG to Paper Mario in other regions. All of this had to happen much later than the release in Super Mario 64.
"Mario Story" itself also changed multiple times throughout the game's development. It was originally Super Mario RPG 2, which was changed due to legal issues; Super Mario Adventure was an intermediate rename. In a 1997 interview with Shigeru Miyamoto, a year after Super Mario 64's release, the RPG was still named "Mario RPG 2".
A secondary interpretation of the plaque texture was that the top line reads "Eternal star", a name that would later be used by the final Mario Party board. Though less useful for speculative purposes, this interpretation arguably makes the most sense as the plaque is on a star-shaped statue. The font used for in-game dialogue also appears to match the "Eternal star" reading. However, the spacing of the letters makes this reading more closely resemble "E te rnal star".
Giant dead Dodongo...
In The Legend of Zelda: Ocarina of Time, a sign using the same texture reads as follows.
Giant dead Dodongo...
when it sees red,
a new way to go
will be open.
This is a hint for a puzzle in the Dodongo's Cavern dungeon. The solution is to throw bombs at the eyes of a giant Dodongo head, making it "see red", to unlock a door.
Some players have attempted to relate this message back to the statue in Super Mario 64. Their reasoning is that a giant undead enemy (the large Boo in the same courtyard as the plaque) drops the entrance to Big Boo's Haunt when Mario (who wears red clothing) defeats it. Even if this stretch of a double meaning were intended, it would have been a roundabout way to tell players how to simply enter a major course in another game.
In addition, it is improbable that the nuances of perceived double meaning are present in Ocarina of Time's Japanese script—though it is still something to potentially look into. If this is the case, then for this theory to still make sense, the English localization team had to have been cognizant of the texture of the sign from which this specific line would be read, and to have the requisite knowledge and intent to mess with a few overly analytic Nintendo fans.
Pit Mario xy
While most less-popular interpretations involve the top line of the plaque, an interpretation of the bottom line as "Pit Mario xy" is recorded in a "Super Mario 64 Mysteries Guide" by a Josiah Plummer. Internally, the game uses the y-axis as the name of the vertical axis; so this reading suggests that the player have Mario fall into a bottomless pit on a vertical Cartesian plane to unlock a secret.
This reading is relatively unhelpful, given that the point of the game was to be in full 3D, with horizontal-and-vertical movement along a world axis being unrealistic for real-time players to accomplish. Another problem is that the world axes and units are invisible, since the game uses polygons instead of tiles. On a more specific note, Big Boo's Haunt does not include any pits, other than the hole leading to the basement.
The guide linked above reasons, "If the text actually is a command to take Mario to a specific location, a z-coordinate is needed." While this is true, this interpretation does not give an x- or y-coordinate, either, which would make the inscription useless.
Confirmed existence of Luigi
On July 25, 2020, 24 years and 1 month after the release of the original game on the Nintendo 64, the source code of Super Mario 64 was leaked. In this leak, never-before-seen files of models and textures of Luigi were found, thus confirming his actual existence within the game, at least via source code.