The game contains a character select portrait for Marie, the games final boss, suggesting that there were plans for her to be a playable character. She was later included as a candidate in a DLC voting campaign during a 2013 Indiegogo fundraiser, but lost to Eliza and Beowulf.
Contributed by MeleeWaluigi
The "Politician Double" voice pack has a few specific pop culture references, including:
•The popular internet meme, "MURICA!"
•"WE'LL DO IT LIVE!", from Bill O'Reilly's infamous breakdown.
•"GREAT SKULLGIRL OR GREATEST SKULLGIRL?" is a reference to Steven Colbert, who jokingly asked if George W Bush was a "Great President or Greatest President?"
•"YOUR LIFE WAS FAIR AND BALANCED!" is a reference to the infamous Fox News slogan.
•"I DID NOT HAVE PUGILISTIC RELATIONS WITH THAT WOMAN!" is a reference to Bill Clinton's response after being accused of having an affair.
•"FOOL ME TWICE...uh...um...WON'T GET FOOLED AGAIN!" is a reference to Bush Jr. failing to remember the saying in a similar fashion.
•"HELP CONTROL THE PET POPULATION! HAVE YOUR PETS SPAYED OR NEUTERED!" is a reference to The Price is Right, when the host would say this exact line.
Contributed by mattwo
In Fukua's story mode, the boss fight with Filia will always be set to Nightmare difficulty no matter what difficulty is chosen.
Contributed by MeleeWaluigi
Eliza is based and named after 2 people: Elizabeth Bathory, a Hungarian Countess and serial killer who believed that by using her victim's blood she would remain beautiful, mirrored by Eliza's own use of blood, and Elizabeth Taylor, the actress who played the title character in the 1963 film, Cleopatra.
Contributed by MeleeWaluigi
When Filia beats Robo Fortune she will say "does she dream of electric mice?", a reference to the science fiction novel "Do Androids Dream Of Electric Sheep?" By Phillip K. Dick.
Contributed by MeleeWaluigi
The Diamond Deflector, a special move that Cerebella can do, is the only attack in the game that can reflect projectiles.
Contributed by MeleeWaluigi
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During the indiegogo campaign for Skullgirls Encore a reward was given to anyone who donated 1,000 dollars, the reward was to submit an NPC character to be included in the game.
Animator "Zone", who created Zone-tan and also worked on the game, was one of the "Patron Saint" backers. Zone-tan later appeared in the Glass Canopy stage.
Contributed by CLXcool
In River King Casino, it's possible to see Yuzuriha from Under Night: In-Birth, Matt and Woolie from the web series "Two Best Friends Play", and two dogs dressed as Chun-Li and Guile from the Street Fighter series.
Contributed by Psychospacecow
One of Beowulf's blockbusters involves performing three uppercuts that each create an image of a howling wolf, which launches the opponent in mid air. After that, an image of a moon appears as he performs a body slam on the opponent. This is a reference to the infamous Three Wolf Moon T-shirt on Amazon.com.
Contributed by Noaxzl
The stage Gehenna is named after a place outside ancient Jerusalem where the worshippers of Baal had child sacrifices and was described as "filled with the blood of innocents".
Contributed by Psychospacecow
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After finishing the story mode of a pirated copy of the game, a notice will pop up saying "What is the square root of a fish? Now I'm sad." This was most likely added to confuse pirates.
Contributed by gamemaster1991
Skullgirls has a Guinness world record for most frames of animation per character. It has 11,515 frames of animation for its 8 playable characters (DLC characters not included) which is an average of 1,439 frames per fighter.
Contributed by Makzu
The game was originally planned to have alternate endings for Story mode for most of the cast except Double. There is unused text of these alternate endings complete with dialogue for what appear to be choices the player would make.

Filia: Would wish for her memories back despite Samson's protests

Cerebella: Asks the Skull Heart to make Vitale Mecidi love her and only her. When she returns home, however, Vitale has gone mad and murdered everyone present except Feng just so he can have Cerebella all to himself. Feng kills Vitale only for him to get back up, turned into a monster. Cerebella and Feng flee to the country, hoping to start a new life.

Peacock: She wastes time making inane wishes that the Skull Heart could not possibly grant, much to the Heart's annoyance.

Parasoul: Seemingly kills Umbrella to prevent another Skullgirl from being made. Umbrella reassures her with her dying breath that she did the right thing.

Ms. Fortune: Goes ahead with her original plan to revive the Fishbone Gang. They are revived as mindless servants of the now Skullgirl Fortune.

Painwheel: Wishes for "Freedom". The Skull Heart frees her from human emotion and restraint, making her into an incredibly powerful Skullgirl.

Valentine: Seals the Skull Heart away to prevent it being used again knowing that it can't be destroyed so easily. However, when she faked a deception against Brain Drain, she killed a character named Christmas, who was close to Brain Drain. For the sake of revenge, Brain Drain forces a control mechanism on Valentine and turns her into the same abomination as Painwheel. As this happens, the Skull Heart mocks Valentine's efforts.
Contributed by MightyKombat
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When using Cerebella's Lock & Load move, there's a 0.2% chance that a crudely-drawn cat will randomly appear.

This was derived from one of the animators drawing a cat in one of the frames but forgetting to take it out. Mike Z insisted that the cat should remain as an Easter egg, with the staff agreeing on the condition that Mike Z would animate it himself.
Contributed by DeerBoarDude
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Umbrella's design seems to be inspired by the mascot of the salt-producing company Morton Salt.
Contributed by DeerBoarDude
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The Cathedral stage has pictures of Venus and Aeon seen in the stained glass windows. Both characters have only been seen in Double's ending, and had a chance of being downloadable characters during the game's Indiegogo campaign, but they were not chosen.
Contributed by Mass Distraction
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Inside the game's files is an unused graphic with an alternate spelling of Squigly's name. It appears that it was meant to be used on the character select screen.
Contributed by DeerBoarDude
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The scene in Fukua's reveal trailer and story mode where Filia is asleep in bed is a reference to the ending of Super Mario Bros. 2.
Contributed by GhostLight
Fukua was originally meant as an April Fools joke poking fun at Capcom's announcement of Decapre, a clone character for Cammy, being included in Ultra Street Fighter IV. However, due to fan feedback, she got to stay in the game.
Contributed by Mass Distraction
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Parasoul's kid sister, Umbrella, was originally going to be included in the game, but was dropped early on in favour of Valentine and Double to increase the number of combat-capable villain characters. Unused graphics and voice clips for Umbrella can still be found within the game's files.
Contributed by DeerBoarDude
If Big Band wins a fight, he has a chance of saying "I have to go now. My planet needs me." This is a reference to the Simpsons episode "The Itchy & Scratchy & Poochie Show".
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According to one of the artists behind Skullgirls, Umbrella's dialogue at the end of Parasoul's story mode is a reference to Terry Bogard's catchphrase "C'mon! Get serious!" in Garou: Mark of the Wolves.
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The cafe featured in Filia's story, MadMans Cafe, is a reference to the popular fighting game website of the same name. The artwork for the cafe is a parody of the Edward Hopper painting "Nighthawks".
Contributed by GhostLight
The stage "Little Innsmouth" is a reference to the H.P. Lovecraft novella, "The Shadow Over Innsmouth".
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Parasoul's level 3 blockbuster, Inferno Brigade, resembles one of BB Hood's supers from Marvel vs. Capcom 2 and Darkstalkers.
Contributed by DeerBoarDude
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According to Lab Zero Games, the total cost of adding a new character to the game's roster is more than $150,000.

No doubt you've noticed the surprisingly large sum we're requesting to finish Squigly. Believe it or not, this is actually cheap for a fighting game character, and the only reason it's even this cheap is because she's already partially complete, and our staff have volunteered to take pay cuts to try and increase the odds of meeting our goal.
Contributed by ThisGuyInTheSuit
Fans of the Hasbro TV show "My Little Pony: Friendship is Magic" set out on making a fighting game called "My Little Pony: Fighting is Magic." Developed by a team of fans called "Mane6," the game would use locales and characters from the show. However, after receiving a cease and desist from Hasbro Corporation, Lab Zero Games added a stretch goal in their Skullgirls Indiegogo campaign to allow the Mane6 dev team to use the Skullgirls engine. The stretch goal was met, allowing Mane6 to continue their game with different assets.
Contributed by RoboBadnik
If Peacock uses the "Shadow of Impending Doom" special, there is a chance that she will drop a steamroller on the opponent, similar to what Dio does when using his stand, The World, in JoJo's Bizarre Adventure. Avery even makes a similar noise when attacking.
Contributed by gamemaster1991
If Valentine loses by timeout, she explodes into a mass of bones as if hit by a Mortal Kombat 3 fatality,with multiple skulls and ribcages.
Contributed by GhostLight
Ms. Fortune's winning quote, "Claws encounter of the furred kind!", is a reference to the 1993 video game Bubsy in Claws Encounter of the Furred Kind.
Contributed by ShyanVixen
Filia's alternative color palettes reference several anime characters, such as Hatsune Miku from the VOCALOID series, Senjougahara Hitagi from animes "Bakemonogatari" and "Nisemonogatari", and Rei Miyamoto from Highschool of the Dead.
Contributed by ShyanVixen
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One of Peacock's crouching attacks, "Curb Your Shoe", kicks the opponent with the Kuribo's Shoe from Super Mario Bros. 3
Contributed by GhostLight
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If Cerebella kills an opponent with her Battle Butt attack, "2000" will appear on screen in a similar fashion as when killing an enemy in Battletoads. This was an intentional reference placed into the game by Mike Z.
Contributed by GhostLight