Quite a few voices were done in-house by Team Cherry (William and Ari) themselves, leading to this situation.
Makoto Koji (an office friend of William and Ari) did most of the voices for the female characters including; Hornet, Mantis Lords, Seer... and Flukemarm!
Creator's Favorite: William states that the Dung Defender is his favorite boss because the fight is so fun. Sadly, it could also be so easy, which is the exact reason why they decided to include an Optional Boss version of him in the Hidden Dreams content pack.
Some NPCs were created by Kickstarter donors, namely Clothnote , Eternal Emilitia, Grey Mourner, Tiso and Tuk.
Tiso was explictly named after the patron who funded the game, Tiso Spencer.
The game also has a secret room where you can read messages contributed from Kickstarter donors.
Cut Song: "Pale Court", an orchestral suite incorporating the White Palace theme and several other leitmotifs, which was released as a bonus track on the Gods and Nightmares soundtrack album.
Descended Creator: Not only did William and Ari develop and draw stuff for the game, they also voiced most of the characters.
Development Gag: In the Tower of Love, one bottled Crawlid corpse had its beta design (it didn't have spikes in its shell) instead of the final version.
All of the four content expansions were given out as free updates. The only paid DLCs that can be bought are the game's soundtracks.
The creators apparently refused offers to license the game to other media (comics, TV show) to avoid overcommercializing it and losing control over its creative direction.
Fan Community Nicknames: At least in the YouTube community, the believers and supporters of the "Hornet is Void" meme have been called "Vornets" or "Team Vornet" collectively (A Portmanteau of the words void and hornet). Yes, a meme about a character's lore is so controversial for comical reasons that it has supporters and detractors.
Follow the Leader: For fans and some media/game journalists, Hollow Knight gets coined as one of the "2D Dark Souls" of the late 2010s given that this is a Homage to From Software's popular game, inspired by having a similar bleak setting, dark lore presented in Story Breadcrumbs, as well as several gameplay mechanics that combine the key features of Dark Souls with the Metroidvania genre. And did you know that there is a line of Hornet that sounds suspiciously like "Git Gud?"
Inspiration for the Work: Despite players and critics comparing it to the genre brought by Dark Souls, Team Cherry has outright stated in numerous interviews that Hollow Knight was inspired by the following:
Faxanadu and Zelda II (Ari's and William's favorite childhood games respectively). Hallownest was created as an inverse of the world tree setting in Faxanadu and the devs wanted to replicate the sense of wonder and discovery brought by their childhood games.
Mega Man X was stated to be one for this game's controls, mainly the Knight being able to dash infinitely (even in mid-air) and the ability to scale up the same wall via the Wall Jump mechanic.
Angel's Egg was one of Ari's main inspirations for the artstyle and atmosphere in Hollow Knight. Dark color palettes and grey shades are common, with faded cities and/or shells placed on walls everywhere in the backgrounds. One of the most obvious similarities are seen in the City of Tears — a dark city constantly under rain, while there is a central fountain with statues in it. Plus, there's also a cracked egg located in the Abyss.
Limited Special Collector's Ultimate Edition: The Collector's Edition includes additional prinited materials and physical products such as a metal brooch, the Quirrel comic tie-in, a gold foil art print set and a collector's box. The Nintendo Switch copies of the Collector's Edition also includes a Hollow Knight-themed cleaning cloth.
Official Fan-Submitted Content: As a part of the reward tier at Kickstarter, backers were able to conceptualize some characters to be added into the game, which were dubbed as "Backer NPCs" by Team Cherry. The first Backer NPC was Cloth, by Noah Sturtridge, and many other characters later followed, most of which are the Ghosts that you can use the dream nail on.
Prequel in Another Medium: The Quirrel Comic depicts some events before Quirrel arrived to Hallownest. In contrast to the game wherein the first time you see Quirrel, he's already inspecting the Black Egg Temple.
Refitted for Sequel: Hornet was supposed to be a second playable character for the base game. Then Team Cherry surprised fans by announcing that Hornet's campaign will be a new title instead, in Hollow Knight: Silksong. Those who backed this game on Kickstarter were also promised to receive the sequel for free.
Release Date Change: Hollow Knight was supposed to be released on June 2015, but due to some circumstances regarding changes in scope, development (notably in transitioning the game's engine to Unity) and content, the game finally came out in Feb 24, 2017.
Bug Fables: There are some obvious references to Hollow Knight, such as a room with a rusted nail and some flowers◊ (referencing the Knight's first weapon, and the Delicate Flower quest respectively). Even this line from Vi references what Millibelle does after scamming you.
Vi: Hmph. What if after we put in a huge deposit they just steal our money and run to a hot spring or something!?
MO: Astray: The King of Inhabitants' battle has very similar mechanics to that of Hollow Knight's Hornet.
One Step From Eden: Ice Needle fires an icicle which pierces through enemies, then after going off the screen, comes back for another piercing shot. Its tooltip reads "SHAA!", a reference to Hornet from Hollow Knight, who has an attack where she throws her needle and then pulls it back using a thread.
The Adventure Pals: The last page of the sticker book contains characters from other games, including Hollow Knight.
The Owl House: In the opening, some of the plush dolls in King's pile include the Knight.
From the Reddit AMA, Team Cherry stated that they do not know how the Knight escaped the Abyss (when its gate was sealed in the first place).
Someone wanted to confirm from the same AMA if Hegemol is actually Sly since the former was believed to have went into hiding. The latter was the most probable candidate whom the fanbase thought that Hegemol may have disguised himself as. William's answer to that was merely "!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!", seemingly dodging the question.
An interviewer from Kotaku asked what happened to Quirrel in the Blue Lake. Team Cherry's answers were just "I dunno" and "Yeah, we're not sure". Although Quirrel's situation there is one of the many plot points that are ambiguous and open to interpretations, fans believe that he died, as referenced by the achievement you get from sitting with him at the Blue Lake." The asset that most point to as proof of this — "quirrel_death_nail" — is not evidence towards his fate, as it is an asset which is also used in other locations.
Similarly Named Works: The "Gods and Glory" DLC had its name changed to Godmaster because there's already a mobile game named Gods and Glory. A month before the DLC came out, the name change was done in order to avoid copyright concerns, but fans and several online media already hyped for the initial name until they got used to the final version.
Sleeper Hit: Team Cherry was known at that time to be a small indie group and had to partner with other development teams when porting and releasing the game (such as how they worked with another developer when transitioning to the Unity Engine, as well as with Jump Shark for this game's Nintendo Switch port). Development was partially funded with Kickstarter with a goal of 35,000 Austrailian Dollars, and fortunately reaching 57,000 at the end of 2014. But behold, for a new indie IP, it has sold 250,000 copies in its first 2 weeks on the Nintendo Switch, and as of February 2019, had sold over 2.8 million copies on all of the platforms it's released to.
Team Cherry answered that they were "dead serious" in adding the secret ending involving Mister Mushroom, implying that he isn't a Joke Character and that his journey is far from finished.
We could get more of Zote in the future, since he has a habit of turning up in strange places.
The Danza: Some of the NPCs are named after the Kickstarter backers who designed them, e.g. Tiso by Tiso Spencer, Joni by Joni Kunelius, and Marissa by Marissa Brice.
When asked who their favorite enemy is in terms of design, William answered "Primal Aspids", and that they are the best enemy in the game, and that they have an idea for a boss version of the mook that sadly didn't make it into the game... "yet". Considering that they are aware of the Primal Aspids' Demonic Spider status and have been memed so much by the community, this answer could just be satirical.
One of the advertised features of the Godmaster update was "expanded romance options". Some took it literally as a Romance Sidequest. Nope, it was revealed that you can just give the Delicate Flower to more characters... nothing romantic involved. Nonetheless, the "Romance Options" phrase became a meme afterwards.
Urban Legend of Zelda: A popular rumor is that Myla could be saved from the Infection by giving her a Delicate Flower before she turns hostile. However, the Delicate Flower itself can only be obtained after getting the Desolate Dive, where obtaining the upgrade infects her anyway. Modders have proven that hacking the Delicate Flower into the inventory before getting Desolate Dive shows that Myla has no additional dialogue if the player somehow gets a Delicate Flower and doesn't react to it. That hasn't stopped modders from taking this rumor and making it a reality, which has caused the rumor to spread even further.
Word of God: From thesetwo AMAs on 2017 and 2018 which answer some of the lore-related theories and game design decisions made by Team Cherry:
The Player Characterdoesn't have a distinct name in-game, only going by the nicknames other characters give it. However, the community uses the title that Team Cherry commonly uses when referring to the playable character, "the Knight".
It is stated by a member of Team Cherry that there is a name used in place of "The Knight" for translations, however the name itself isn't known.
The playable Knight was drawn back into the kingdom, which is why the game starts off from the Howling Cliffs, despite the Knight being created by the Pale King. However, they didn't go into details explaining why the Knight left the kingdom and where he went prior to the start of the game.
The reason why the enigmatic Mister Mushroom was made? It's because Team Cherry felt that the unique nook Cornifer used to be in the Fungal Wastes would be left empty and sad if he moved. They needed someone to put in that nook again, and it became Mister Mushroom's first point of appearance.
Hornet and the Hollow Knight do have some sort of relation to one another. As the Hollow Knight is the creation of the Pale King and the White Lady, where Hornet is the creation of the Pale King and Herrah the Beast, this makes them half-siblings, though perhaps not biologically. This is corroborated by the second ending, "Sealed Siblings."
Hornet is fully limbed, her arms are simply obscured. Exactly how many arms she has is unclear though.
Hornet's needle is unique, it was made for her, and that there aren't many other bugs skillful enough to use it.
Quirrel is "gone", but if he's dead or simply travelling somewhere else isn't clarified.
The Failed Tramway was an attempt of the bugs of Hallownest to expand the kingdom into unknown territories below. Unfortunately, things didn't work out well for them.
As for Cornifer appearing in all areas, most of which are hazardous and deadly, it is stated that his sturdy shell keeps him out of harm's way.
While the Pale King is explicitly identified as a "Wyrm" of a Higher Being, the base game never outright told us what kind of a Higher Being is the White Lady... Until William explained that she is a "Root". In The Grimm Troupe DLC, Grimm does have a subtle reference to it, mentioning "worm and root" as the kingdom's rulers.
Sly mentions the name "Esmy" when you first meet him. William states that Esmy is someone that still lingers in Sly's dreams.
Jinn is confirmed to be female.
To those who mishear and can't understand some of the fictional language of the bugs, Iselda's exasperated sigh is followed by "Bapanada", while the Battle Cry of the Dung Defender is "FAAAAAAARRRFFUUUUNNNDADDAAA"!
Based on what's seen in the game, it's not clear whether the bees in the Hive are infected or merely protecting their nest and their queen, but according to Team Cherry they are indeed infected.
Working Title: Hungry Knight 2. Back when development started, Team Cherry re-used the assets for their previous game Hungry Knight and the code for Lulanda (one of William's early platformer games). This title was scrapped because the Knight doesn't eat anything anymore. There are some Mythology Gags here that clearly refer to Hungry Knight though.
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