Cowboy BeBop at His Computer: Bizarre in that it comes from an official Bungie product. The Mac Action Sack's synopsis for Marathon 2 claims that "it's time to settle the score with Durandal, your old nemesis from Marathon"; not only is there no point in the game where Durandal and the Security Officer are at odds, but Durandal underwent a change of heart between the first and second games. (It is entirely possible that this was to avoid spoiling M1 for new players, though.)
Executive Meddling: The reason that only Marathon 2 has an Xbox Live Arcade port: reportedly, Freeverse and Bungie wanted to port all three games, but Microsoft vetoed it.
Fan Nickname: Various characters, enemies, levels, etc. have them.
The Security Officer is usually referred to as "Mr Marathon" by members of the Discord server. The origin of it isn't entirely clear; Discord member Mr. Theta claimed to have originated it, but later claimed to have stolen it from someone else on YouTube. One might expect the protagonist of Pathways into Darkness to be "Mr Pathways" by extension, but "pidbro" or "pidpal" are more commonly seen, for reasons not even the Discord users might be able to explain. The Marathon community has no similar common nicknames for Master Chief.
Assimilated Bobs are A-Bobs or Assbobs.
The term "flappy bois" for Ticks, apparently coined by engine developer Treellama, has been seeing increasing usage in recent months, to the extent that the Discord server now uses :flappyboi: as the code for its Tick emoticon.
"STFU jump" is sometimes used for a particularly difficult jump mandated by the speedrun route for the level "Six Thousand Feet Under", as a pun on a common Internet acronym that usually has another meaning. Part of this is just because it's funny, and part of it is because the jump can be a run killer. (We should note that by no means all runners abbreviate the level as "STFU"; some abbreviate it as "6K feet" or similar instead.) "Where the Twist Flops", by extension, is occasionally seen as WTF (this is less common, and usually only seen in combination with the previous acronym, though).
A particular image◊ of Bungie lead programmer Jason Jones, as Robert Blake, giving a "thumbs up" is sometimes referred to as "fun Robert". This apparently originated as a reference to the tags for the MapDamager.lua script, which were set as "fun" and "robert" for reasons unexplained.
Jossed: A minor example regarding the simulacrums. Most of the things they shout are coherent, if strange in context, but "frog blast the vent core!" is a dead giveaway that they're not actually human; it also sounds just enough like a corruption of a normal phrase that fans spent some time trying to puzzle out the source. Per Doug Zartman via the Marathon Scrapbook, the guess that it was "God bless the Marine Corps." is good, but ultimately wrong—it was just plain old random nonsense on his part.
The Story Page's "Red Sand" section, written prior to the release of Marathon 2, posits that the S'pht homeworld might have actually been Mars; it also discusses a sub-theory that the voyage of the UESC Marathon was secretly a first-contact mission. Of course, as the page's final revision notes, in the actual game Lh'owon and Mars are completely separate planets.
Keep Circulating The Tarballs: The Aleph One project, ensuring that Marathon would go on with or without Bungie's guidance (currently with, since Microsoft spun Bungie off again).
Promoted Fanboy: Many, such as Craig Mullins (who would go on to be concept artist of high renown himself), Randall "Frigidman" Shaw, and Tuncer Deniz.
Hidden levels in the first game featuring such pleasantries as invincible, wall-climbing red Drinniols; the most well-known level title is "A Good Way to Die". Posited by the otherwise-accurate "Marathon Secrets Guide"; after the Trilogy was ported over to Aleph One, a few scenario makers borrowed and defictionalized these concepts.
Dr'At'Er, a supposed fourth entry running on a proper 3D engine; one website claimed to have screenshots, which were actually altered from Quake. The giveaway? The title's a reversed slur.
Marathon Gold, a collection of the Trilogy and a few well-known fan scenarios that was mentioned in a supposed Bungie newsletter. It, too, was a false rumour.
What Could Have Been: The original plan for the first game called for the plot to branch at various points depending on how many BoBs you saved in certain levels. This was scrapped and the only remnant of that plan is differing messages from Leela depending on how many of them you saved.
It is worth noting that the capacity to do this was still built into the engine, and that when a player transitions from the end of one level they can (in theory) be sent to any other map-maker defined level in the game, regardless of level order. While conventionally the player is sent to the next level in the order, some mod-makers have taken full advantage of this ability to alter the next level that the player goes to based on what they accomplished in that level, with resulting branching plotlines. Rubicon is the most famous but by no means the only or even the first example of a mod that does this.
The alpha version, which could be described as Pathways into Darkness: Space Edition, was set not on a ship, but a hollowed-out asteroid near Pluto; the Science Officer is sent to investigate the disappearance of this asteroid's colonists and finds only feral aliens.
A later draft had colonists uncovering a strange device that turns out to be a Trojan Horse for the nearby hostile aliens; by the time the Science Officer arrives, things are looking very dire.
One screenshot from a build between the alpha and the final shows a compass and injury-tracker integrated into the HUD; both were dropped, with the reason given for the former being that it required more horsepower than most Macs of the time could spare. We can get an idea of what the compass would've been like with Eternal, which implements the idea.
Three enemies were cut from the first game: the Hound (a pet for the Hunters that couldn't climb stairs), the Pfhor crewman (harmless stilt-bots that were the alien equivalent to the BoBs), and the Armageddon Beast (a nasty-looking Boss in Mook Clothing). The crewman was dropped due to memory limits, and the Beast got the boot because no levels were designed such that it would actually be fun to fight.
While it's possible that this was always meant to be temporary, in the original level notes for Marathon 2, Durandal is consistently polite to the Security Officer and shows few/no traces of his earlier instability. This doesn't stop Tycho (himself not quite as big a jerkass as in the final) from trying to cast doubt on his brother's true intentions.
The level "Foe Hammer" was originally meant to have drones firing at you from the outside windows, but this idea was dropped because drone corpses kept littering the landscape (though it still could've been avoided if they'd lowered the floor of the outside polygons, kept them space-textured, and changed the monster physics of the drones to make them climb greater distances). Several levels that weren't vacuum levels in the final game, including this one, were also originally intended to be vacuum levels, though in this case this may have been for the best since the one-two punch of "Acme Station" and "Post Naval Trauma" were already punishing enough. But that's why you see oxygen rechargers in a lot of levels that aren't vacuum - plus why Tycho tells you to "drink vacuum" when, of course, you don't lose any oxygen after he teleports you out to space.
"Naw Man He's Close" also seems to have been initially constructed with a climb up a control tower above Pfhor slime. The map was substantially revamped before the final release of the game, and the tower didn't make it in. "One Thousand Thousand Slimy Things" was also intended to feature a climb up a tower, but this was scrapped because it was considered too similar to the one in Marathon 2 ("The Hard Stuff Rules..."), which was deemed architecturally more interesting.
While this hasn't been explicitly confirmed, the architecture of "Come and Take Your Medicine" certainly makes it look like the level was never entirely finished - it's only necessary to explore a small portion of the level in order to complete it. It's possible Bungie just didn't have time to finish touching it up to make more of the architecture relevant to the mission before releasing the game. Also unusual is that it's a gigantic water level with no oxygen recharger. However, there's also the Alternate Character Interpretation that all of this was intentional as a form of Character Development for Durandal: he tells you there's no reward to exploring the rest of the level, and unless you enjoy fighting Troopers, there really isn't, at least in single-player games; the only items of any real value to be found anywhere in the level are the first alien weapon (the next one to be found is a couple of levels later, in "Ex cathedra") and a small amount of ammo.
"Ex cathedra" initially featured a much more complicated puzzle before swimming was introduced into the game engine - it was initially necessary to make some skilled jumps in order to navigate the level. Once swimming was introduced, this entire puzzle became superfluous.
Greg Kirkpatrick himself considers "Charon Doesn't Make Change" one. He says that if he'd had time to think about it, he'd have doubled the size of the level and made it gigantic.
The original level notes for Marathon 2 would have resulted in a very different game in several important ways. Several enemy types are listed that didn't make it into the final game, and several levels would've been vacuum levels (the final game didn't contain any vacuum levels at all). A lot of levels would've been in a different order or had different titles, and several terminals were unsurprisingly rewritten significantly for the final game; in particular, Durandal's survival after "Begging for Mercy Makes Me Angry!" would've been revealed almost instantly. There also would've been a secret level at the end entitled "Never Eat Yellow Snow" (a possible Shout-Out to a Frank Zappa song from Apostrophe (')) that would've contained Pathways into Darkness textures and monsters. The level notes also make it clear that Bungie had the idea for VacBobs early in the development process of Marathon 2, but they only actually made it into Infinity.
A PlayStation port of either Marathon 2 or Infinity was under consideration at one point, and canned for unknown reasons.
Despite what some people would tell you, Infinity is not "Marathon 3". An actual project titled "Marathon 3" was in development for around two months before being supplanted by Myth: The Fallen Lords; the short version is that Bungie didn't really want to chase Quake's tail. Only one possible asset of M3, a single image of Durandal's face (under June 21), has been uncovered thus far.
RyokoTK made Phoenix with the intention for speedruns to be possible, and expressed approval of a fan's 37-minute speedrun when it was completed.
Ascended Fanboy (or Ascended Fangirl): In some cases, new revisions of mods have been co-developed by people who were already fans of the earlier releases. Examples include Eternal and Tempus Irae.
Attention Deficit Creator Disorder: Some developers can suffer this. One particular developer has contributed in some fashion to Eternal, the revised Tempus Irae, Where Monsters Are in Dreams, the revised Apotheosis, his own mod called Marathon Chronicles, remastered sounds for Marathon 1 and Marathon Infinity, and a YouTube channel he maintains with thousands of videos. Most other developers aren't this severe about this, but this trope has no doubt contributed to some of the Schedule Slips various mods sometimes see.
Creator Backlash: The creator of Phoenix, although not too critical of the game overall, has been rather dismissive of the game's story. He also doesn't much care for the level "Escape Two Thousand", owing in large part to the mixture of combat and precise jumps the level requires to complete successfully.
Creator Breakdown: One of the reasons that Eternal 1.2 was delayed a few months past its original planned release date, and that future release of Eternal are now virtually certain to happen, is that one of its developers suffered one of these in early 2019, meaning that several planned features were ultimately held for a future update.
Development Hell: Since many scenarios are the works of small numbers of amateur creators who are often perfectionists and have other commitments besides game development, they don't go as quickly as commercial development projects. Some scenarios such as Where Monsters Are in Dreams, Marathon 1 Redux, and Marathon Chronicles have been in active development for years or even decades. Sometimes creators will release incomplete versions of their games, but sometimes all you get are screenshots or gameplay videos. At the same time, in the best cases, this may end up being a blessing in disguise, because some of these scenarios have ended up being very detailed and refined, particularly if creators keep going back and revising the games in response to player feedback (as has happened in Eternal's case). On the other hand, sometimes you end up with Orphaned Series; Megiddo Game and Return to Marathon are particularly infamous cases of this, since what we did get was so good (Megiddo Game even won Bungie's mapmaking competition. Its creator was later one of the two main people behind Tempus Irae, though, so it wasn't a complete loss).
One of Us: Obviously you'd have to be broadly a case of this trope to make a Game Mod, but a few people who have worked on various mods such as Eternal are known to edit the TV Tropes wiki, although their names are being omitted for the sake of privacy. (This means that some, though by no means all, of the info on these mods here is Word of God or Word of Saint Paul.) Several other scenario creators have also referred to various tropes by name. Many of the creators are also, unsurprisingly, active on the various Marathon-related forums and Discord servers out there, and some of their posts have been cited on this very wiki.
Saved from Development Hell: Eternal has had a lengthy development cycle that has lasted for some fifteen years as of this writing and is still not complete, as seen on its development page, which lists all the release dates. The first version of the game appeared in late 2004. Version 1.0 came out in 2008, 1.1 in 2015, and 1.2 in 2019. Several of these suffered Schedule Slips for various reasons; version 1.3, formerly 1.2.1 before it was renamed due to the number of new features it contains, is currently in development and likely to be released in mid to late 2020, with version 1.4, likely to be the final major update of the game, planned for release after that.
Throw It In!: Sometimes features of level design are the result of happy accidents. "Killing the Giants as They Sleep" in Eternal 1.2 is a composite of two levels from earlier versions of the game, "May the Pfharce Be With You" and "Forever My Greatest and Only Love". The latter was removed from 1.1 due to a story rewrite, but the two levels were combined into one giant level, the largest in the game by polygon count, in 1.2. The happy accident is that both of those levels centred around an octagonal architectural structure featuring the ubiquitous Pfhor slime, which "Killing the Giants" takes full advantage of by stacking them on top of one another, but it's unlikely the designers of the original levels had this in mind when making them, since they originally weren't even intended to be part of the same ship. Regardless, this particular design accident helps the two segments feel more like part of the same space. It also helps that the two levels have fairly similar architectural styles (partially because the same designer designed part of "May the Pfharce Be With You" and all of "Forever My Greatest and Only Love", and partially as a joke on the stagnancy of Pfhor culture: their architecture hasn't changed meaningfully in some 10,000 years, as shown in the chapter four Pfhor ship levels).
Unintentional Period Piece: Eternal is arguably a downplayed case, as the War on Terror (topical when the game first appeared in 2004, but less so now) was an inspiration for a major subplot of the game, but like many other aspects of the plot, it's done quite subtly and still has applicability to other real-world events. The increased prevalence of authoritarianism in modern politics has arguably made some aspects of its message timelier in 2019 than they were in 2004.
Not so much one for Eternal on its own, but for Halo: Eternal's implementation of the Jjaro was originally meant to tie in with the story of Halo, before the latter was rewritten to remove most of its connections to the Marathon universe. It would have been interesting to see how they'd have interlocked had that plan not been abandoned.
The creators of Rubicon have admitted that the terminals could have tied in better with the level missions if they'd taken another week or so to rewrite them once level development had finished.
Eternal's director had quite a few things he'd have done differently in hindsight. A 1.3 version is planned and may still implement one or two of these ideas, though many of the others would require a complete redesign of the game from the ground up. Ultimately, Eternal could still be considered part of a loose trilogy with Phoenix and Rubicon as parts two and three (Kindred Spirits actually links the latter two, though it's only four levels long). However, this still leaves several major plot branches unresolved, potentially to be explored in future games. (One of the main developers of the current 1.2 release is in fact working on a game that plans to do this entitled Marathon Chronicles; info can be found on the Pfhorums or YouTube. It is available as a currently roughly half-finished game, although very little of the planned story is yet implemented in the game itself.)
A less substantial case for Eternal is that version 1.2 was initially planned to incorporate rain, snow, and various other effects on some levels, but this wound up causing lag on some older machines. The engine didn't provide any way to make these effects optional at the time of release, so instead they were released separately as the "precipitation branch" of the game. It can be found on Github or on Simplici7y (note that, despite the URL, the latter is actually the current beta of 1.2.1).
At one point, the creators of Eternal and Rubicon considered merging their projects. In a way, it's probably good that they didn't, though, because it's unlikely the combined result would've been longer than either game was by itself.
The old Rubicon site, as well as some of the game's secret levels, detailed the history of the scenario and what was intended for the smaller ones that became part of it. "Chimera" (which became the final's Chimera Plank) would've involved the eponymous ship crashing on Pfhor Prime as it does at the start of Rubicon, except this time it was seemingly part of an ancient Pfhoric prophecy, and in the chaos the player would've found themselves teaming up with a Pfhor AI, Usyrus. Another scenario, from which some plot elements in Rubicon's Salinger Plank originate, wasn't meant to be part of the Marathon universe.
There are six bonus levels at the end of Phoenix 1.3 that represent what was to be the first chapter of an abandoned project entitled Thunderstorm, based around the idea of shorter levels that would mostly have been focused around exploration and combat. Ryoko abandoned this idea and placed them as secret levels that can be accessed from the secret terminal of "Swan Song"; he is now working on a Metroid Prime-inspired mod entitled Echoes of the Ashen instead.
Working Title: Tempus Irae's levels had the following working titles:
"Wiping Away the Dirt & Glue" was known as "Sistine Chapel"
"Sordidae, turpes et faetidae" was known as "Streets of Milan"