Beam Me Up, Scotty!: People quoting Andre's parting words to player often cut his two lines down to "Don't go turnin' Hollow."
Bilingual Bonus/Multiple Reference Pun: At the end of the prologue, the player is carried to a different part of the world by a giant crow, which many suspect is in some way related to Velka, the goddess of sin, who is associated with crows in the lore. In Czech, the word "velka" is a feminine form of "velky", meaning "large". The word for "crow", "vrana", is feminine, meaning that it's used with the feminine form of adjectives. A "large crow" is therefore "velka vrana".
Breakthrough Hit: Demon's Souls was a Sleeper Hit and a slowburner that slowly built up in popularity through good word of mouth and critical acclaim in the west. Dark Souls on the other hand was an instant hit, selling 1.6 million copies within the first month, 2.367 million by 2013 and helped put From Software, a Japanese developer with a small cult following in the states, on the map as a developer of great, hardcore titles. It was also a Breakthrough Hit for director Hidetaka Miyazaki, who was only credited in three games before he got notoriety for his work with Dark Souls and Demon's Souls. Even he was shocked by how much press and requests for interviews he suddenly started getting. Not bad for a niche title from a small developer.
Colbert Bump: The Silent Comedy received this when their songs, Bartholomew and All Saints Day, were featured in a couple of trailers for the game.
The two Souls games also help spark up interest in FromSoftware's King's Field series, which never caught on in the states.
Dueling Games: Despite being a month apart, Dark Souls has a rival in The Elder Scrolls V: Skyrim, with both being the top RPGs coming out in 2011's fourth quarter. Fans of both series groaned at news outlets trying to play up this conflict in spite of the games' numerous differences.
Darkroot Garden and has been dubbed Dickstab Garden due to Forest Hunters constantly invading players. Forest Hunters themselves are sometimes called "Park Rangers" for the same reason.
Sunbro and Brolaire for Solaire of Astora due to him being a great help in boss battles and Onionbro for Siegmeyer of Catarina due to his helmet looking like, well, an onion. The Sunbro nickname has spread to all the players that joined the Warrior of Sunlight covenant, as that puts an emphasis on "jolly cooperation!" Players also glow a bright gold, the same as Solaire has. Siegmeyer's daughter is often called "Onionsis" by association.
In a similar vein to Solaire and Siegmeyer, Laurentius of the Great Swamp has been referred to as Swampbro and Pyrobro.
Wolfbro, for Great Grey Wolf Sif. Somewhat odd, as the name "Sif" comes from a Norse goddess.
The Official Dark Souls Guide actually refers to Sif as a male numerous times.
This originated from a rumor going around before the game was out that the Great Grey Wolf Sif would be an ally who tested your mettle. A good example of making assumptions isn't ever a good idea, the reaction from it being nothing but a run of the mill boss fight was priceless.
Siegmeyer (or mostly anybody wearing the Catarina set) is known as Onionbro.
Gravelord Nito has been referred to as Papa Nito. Members of the Gravelord covenant are often called Waitlords, in reference to the fact that Gravelording consists of a lot of fruitless sitting around waiting for players you're infected to invade you.
Lautrec is know as Yurt 2.0 and Gold Yurt considering the way you meet him and what he does after you free him.
Anor Londo is called "Anal Rondo" or "Anal Rodeo" by some, in reference to its difficulty(especially the bridge part with Silver Knights firing javelins at you).
The official guide refers to the unseen crow NPC in the Undead Asylum as Hawk Girl, but Sparkly and/or Snuggly are more popular.
Sen's Fortress can be "Sen's Funhouse," or, as the result of a humorous typo, "Super Nintendo Fortress."
Estus is often called Sunny D, because an Estus Flask that still has uses is roughly the same color and shape as a half gallon of the drink.
Members of the Darkwraith Covenant are commonly referred to as "Dickwraiths". In a similar manner, members of the Darkmoon Covenant are sometimes referred to as "Dorkmoons".
Due to one of Knight Artorias' attack in which he throws a liquefied... something of the Abyss that looks like dark blue/black ink, he is sometimes called Knight of the Oil Spill.
In Japan, Xanthous King Jeremiah's infamous turban is nicknamed "Borraginol", after a brand of suppositories sold in Japan. Some Let's Players even go so far to include the Borraginol jingle (cheerfully saying "Borraginol for your hemorrhoids!") when they use the armor.
Flip Flop of God: According to the Dark Souls Official Guide, the Bed of Chaos Guardian's real name is Quelaana, which would fit right in with the prefix convention of the Chaos Sisters (Quelana of Izalith and Quelaag). However, the guide also describes the Bed of Chaos Guardian as a male...
Hey, It's That Voice!: A few voice actors from Demon's Souls return to voice different characters. For example, Frampt and Kaathe are voiced by Peter Marinker (King Allant), Quelana is voiced by Jenny Funnell (Yuria) and Priscilla is voiced by Clare Corbett (Astraea). Alvina is voiced by Judi Dench soundalike Ève Karpf, who, fittingly, voiced M in some of the James Bond games, as well as Minerva McGonagall in the Harry Potter games and Lara Croft's mother in Tomb Raider Legend.
Artorias was voiced by Josh Cohen who played Ostrava from Demon's Souls, but the files were eventually dummied out and left unused. However, data mining in the PC version found them. Prepare to Cry.
Shrug of God: Director Hidetaka Miyazaki's stance on whether the pendant has any secret use in game, though he encourages players to keep looking.
Teasing Creator: Miyazaki is like this; he doesn't say if the pendent has any secret use, but encourages players to continue looking. He states that Ceaseless Dicharge is skippable (He is), before mysteriously stating that maybe he isn't (some of the equipment used to make that run was later nerfed, so it may no longer be possible).
Throw It In: Surprisingly enough, Maneater Mildred. Word of God says that one of the developers invaded during debugging and surprised the rest of the development team. They liked it enough that they got the data and quickly wrote up a background for her.
Trolling Creator: When the game was released, game director Hidetaka Miyazaki hinted that the pendant you could choose as a starting item would be a Chekhov's Gun. A year later, Miyazaki later admitted that the pendant is completely useless since the whole thing was intended as a prank. So basically, Miyazaki tricked hundreds or even thousands of players into choosing a completely worthless pendant as their starting item!
Even better is the nature of this prank. Players would only have to see it to believe there was some use for it, and from there came an endless stream of theories. For that to happen, all that had to be done regarding the Pendant is it had to be in the game, and the very nature of Dark Souls as a game did the rest. Miyazaki played a very elaborate prank by simply putting the Pendant in the game.
Urban Legend of Zelda: Since the game's release there have been dozens of different rumors pertaining to the Furtive Pygmy and the true purpose of the Pendant.
Another persistent rumor claimed that the player has the option to spare the Great Grey Wolf Sif and that you would get his sword as a reward for doing so. No proof or method has been found, but many still believe there is a way to accomplish this. It is possible to technically spare Sif, by using a certain glitch to transfer the Covenant of Artorias to a new character. You get no proper resolution for it, of course.
Quelaag originally had a rather long intro speech which ran from when you entered her domain to when you entered the fog gate for the boss battle. But Miyazaki felt that the script for it was of poor quality and that it took something from her character.
Priscilla was originally supposed to be a major heroine, akin to the Maiden in Black from Demon's Souls. Due to her original role becoming obsolete, she was placed in the Painted World of Ariamis due to the location's winter atmosphere.
Speaking of Priscilla's original role, Miyazaki is tight-lipped about what exactly it was.
On top of that The Painted World of Ariamis that was used for Priscilla was the actual basis from which the Project Dark prototype was turned into Dark Souls. Gravelord Nito was originally supposed to be the area boss instead of Priscilla, with the latter's boss arena actually being a crumbling floor, much like the Stray Demon. After spending so much time creating the area for the prototype, Miyazaki was determined to include it in the final product, but couldn't do it coherently in accordance to the rest of the game world. So he ended up "cheating" and created the Painted World.
The knight that gives you the Estus Flask was originally named Oscar and was intended to be your rival throughout the game, siding with whichever serpent you didn't, instead of dying when you reach up to him after the Asylum Demon. The name used in the strategy guide is the only holdover from this incarnation.
Andre was originally supposed to be a descendant of Gwyn and more imposing, serving as the guardian of the door to the Firelink Shrine. He was also supposed to move the goddess statue found in the ruined temple, allowing the player to progress with the story.
Content that was cut from the game reveals that entering into a Covenant with Velka would be possible. Said covenant was quite possibly merged with or was turned into the Darkmoon Covenant.
When Smough was first conceived, he was originally supposed to be one of the Four Knights. Miyazaki allegedly liked him so much he decided against making him a knight and worked it into his backstory as a heretic who wished to join the Four Knights.
There was Concept Art of Abyss Walker Artorias drawn for the game, indicating he might have made an appearance at one point. He appears in the Updated Re-release, albeit with a different character design than his original.
Gwynevere was based on a character from a manga called Yasaragi no Yakata, or Tranquil Mansion, where members of an exclusive club would have a giant woman care for them as if they were children. One concept was that she had a mouth in the palm of her hand and they made all the animations made for it, but the idea didn't make it into the final game. She was originally going to be more lithe and elegant looking compared to the... voluptuous version that ended up in the game. The artist who designed her was so proud of the concept art when he showed it to Director Miyazaki that the Director couldn't bring himself to reject the design.
Firelink Shrine was supposed to be a water temple: a very healing locale with water, greenery, soft light, and subtle music. As the idea of Kindling and Frampt's arrival developed, the water eventually dried up to what is seen in the final product. Even the bonfire was moved, since the uneven ground of the original placement interfered with the player's sitting animations. The finalized location was originally a small pond.
The boss fight atop the Undead Parish was originally the Demon Centipede, but due to how ridiculous it seemed, the Centipede was moved and replaced with the Gargoyles.
Oswald of Carim was originally supposed to be a woman of age 60, and you were originally supposed to use an Affidavit item, similar to the Indictment item, to leave your current Covenant instead of being able to straight-up ask to him.
By hacking the game and making the debug menu available, one Dark Souls fan found some very interesting character models that were dummied out of the final game.
Of these include an undead clad in bizarre gold armor named "Undead King Jar-Eel◊", a darkwraith with the power of life drain who would have been the boss of New Londo. The Four Kings use a portion of his coding, and even appear to be wearing a corrupted version of his armor. Presumably, he was removed for being too similar to Gwyn, (a tall, humanoid enemy which has become a husk of his former self). Ingward was also supposed to sic him on you as a test to prove whether or not you're worthy of entering the Abyss.
There's also an alternate Bed of Chaos that appears to have been designed as a more traditional boss fight with crawling and jumping animations. Word of God says that the original Bed of Chaos was supposed to have a stronger boss fight concept, but instead became the relatively simple-but-irritating Puzzle Boss due to time constraints that kept the concept from being properly polished.
There are also a few unused enemies like the Brain Bugs and the Claw-Hollows, which we saw fan art for but were never seen in the final game.
A dummied-out "side quest" had you rescuing Petrus from the necromancers of the Catacombs to start his and Rhea's character arc, instead of being able to encounter him from the get-go and starting the arc via ringing the first Bell of Awakening. Although it may have been cut to keep aware players from figuring out his intentions as easily.
Shiva was supposed to be something similar to what happens with Lautrec: he would attack you if you either showed him the Chaos Blade- in an attempt to take it from you - or gave it to him, in an attempt to test it on a worthy opponent. This would also serve as a Call Back to Demon's Souls, in which Master Satsuki would attack the player if they showed him the Magic Sword "Makoto" (or would attack them if they voluntarily handed it over to him). In addition, he was also supposed to be invaded with a Black Eye Orb (as with Lautrec); but instead of retrieving a Fire Keeper's Soul, you were to retrieve the Chaos Blade.
Dusk of Oolacile was originally supposed to summon you to rescue her instead of freeing her spirit from the Golem. The new content plays with and rebuilds this, but you find out that Artorias was the one trying to rescue her. You just get dragged into it.
The triple-shot crossbow Avelyn was originally supposed to belong to Domhnall of Zena before the developers turned it into an elusive treasure. It still shows up as Chester's trademark weapon, though.
Word of God: Developer interviews have shed some light on the story of the game.
Miyazaki has stated that the Pygmy is the ancestor of humanity and that humanity inherited a piece of the Dark Soul through him.
The Gaping Dragon was originally a normal Everlasting Dragon that became corrupted by its own gluttony, causing it to grow a massive maw.
Ceaseless Discharge is confirmed to be the brother of the Daughters of Chaos.
If you kill Gwyn with Solaire as a phantom, Solaire links the fire in his own world.
Kirk is a member of the Chaos Servant covenant.
The ruins in Darkroot forest were originally part of Oolacile. Combines with What Could Have Been. You were originally supposed to be summoned there to rescue Dusk. The Updated Re-release builds on the cut content.
Writing by the Seat of Your Pants: Like many other video games, story comes after the game. Miyazaki has said in interviews that he makes up the lore as he goes along.