[[WMG: Mandy is just a snotty and arrogant girl, and not the Devil or The Antichrist as we suppose her to be.]]
The Devil or The Antichrist are known to possess just one emotion-hatred. Yes,Mandy has lots of it,but she also possesses other human emotions like love, concern, grief, etc. in several episodes, though she doesn't admit it. She often says that she want to rule over the world and make everyone her slave, but she isn't the only person in cartoon history to have this desire. {{Horrid Henry}} in the hit British series of the same name has the same urge to rule over the world as King Henry The Horrid. Mandy is shown to show genuine concern about Billy's health in many episodes. If we consider this factor, Horrid Henry is worse than Mandy as he does not care a damn about his parents and his younger brother(Perfect Peter) in 99% of the series.

[[WMG: Grim and all other supernatural beings were not real... At first.]]
Mandy is so world-shatteringly powerful, that she can blur the line between metaphysical and physical. Luckily, Billy is so world-shatteringly stupid that the various {{Eldritch Abomination}}s come out as the silly, quirky characters they are. If either Billy or Mandy were to die, the universe would dissolve into pure Darkness or Stupidity, as appropriate for the surviving one.

[[WMG: Grim is forced to repeatedly revive the characters whenever they die.]]
Over the course of the show, many of the characters have been seen dying, only to return in the next episode(usually regarded as NegativeContinuity). In one episode, Grim is seen as being capable of allowing someone to live longer by putting more sand into his or her lifetimer. Since Grim is forced to be Billy and Mandy's best friend forever, that could mean that in order to live up to his end of the bargain, Billy and Mandy literally have to live FOREVER, meaning that he must bring them back to life whenever they get themselves killed. When any other characters die, Mandy probably orders Grim to revive them as well so she doesn't lose any of her future minions. And when Grim dies...well, he's the Grim Reaper, so he can probably revive himself.

[[WMG: Being Mandy is UsefulNotes/AdolfHitler's IronicHell.]]
He's a little girl, but the universe underestimated him.

[[WMG:Mandy is the ultimate evil of the multiverse, although she's not ''entirely'' aware of it.]]
This would of course, make her the Main/EvilCounterpart of [[spoiler:Haruhi Suzumiya]].
* And the Anti-Monitor.
** And once she realises this,there will be an epic battle between her and the rest of the Cartoon Network multiverse
* This is a given in a fanwork by the creator of Webcomic/PowerpuffGirlsDoujinshi.
* Well, it seems like she at least knows it to the extent that she can control the whole of Endsville, and possibly beyond (watch the episode where Grim and Billy call the Nanny on her).
** No, you've got it all wrong. She's the EvilCounterpart of WesternAnimation/RubyGloom. Seriously, they're complete opposites in every conceivable way.
* Eons ago, an UltimateEvil once dominated the underworld, having near-absolute control. It had total control over death, so it was immortal. It was also immune to almost any form of karma. One of Grim's ancestors managed to defeat this evil, by trapping it in a mortal body. However this being swore that, if it ever saw one of his/her ilk, it would have his revenge. Mandy was the ultimate result: This UltimateEvil had passed its essence down generation after generation, until it reached her. Mandy was naturally moody and somewhat sociopathic to begin with, so the moment she won the bet, the UltimateEvil began to awake. Luckily, Mandy only contains the soul of this being and not the memories, so she can't fully access her dark powers. Her parents weren't terrified of her until her dark powers awoke, and though Grim reaped her ancestors, he never was close enough to them to trigger this.
** Alternate theory: She could very well be [[WesternAnimation/SamuraiJack Aku]], who after Samurai Jack returned from the future and struck the final blow, what remained of Aku transferred itself into a mortal body, which passed on for generations since.

[[WMG: Mandy is the reincarnation of Chernabog]]
Remember [[http://en.wikipedia.org/wiki/List_of_The_Grim_Adventures_of_Billy_&_Mandy_episodes#Season_1:_2001 "Dream a Little Dream?"]] That wasn't a nightmare. That was a past-life memory.

[[WMG: Mandy is Eris' daughter]]
Her adoptive parents didn't really know how to pronounce and/or spell Dysnomia, and then, just named her Amanda... Or just Mandy, anyways. That's why Eris is so much time around them, even for being a deity. And Dysnomia was, indeed, smarter than her mom in the original mythology.
* So that's where she got her blonde hair.

[[WMG: Mandy ''and'' Billy are Eris' children.]]
Billy is [[ChaoticStupid chaos and discord]] in his own way. Billy is actually Mandy's half-brother, concieved by Eris [[GenderBender taking a male form]] when meeting [[LesYay Gladys.]] Unlike Mandy, Billy is only half-divine and thus is only able to indirectly access his powers. Mandy is an EnfanteTerrible supreme because she has more powers than Billy and knows how to use them effectively. Having them trick Grim into being their friend forever was a gambit by Eris to [[DeathTakesAHoliday screw with laws of life and death]].

[[WMG: Grim, his granny, and Nergal are secretly high-class chefs]]
Why else would their food be so goddamn delicious?

[[WMG: The ''Literature/GodEmperorOfDune''-esque future where Mandy has enslaved the world '''might''' have been averted...]]
...If only Grim hadn't [[NiceJobBreakingItHero revealed it to Mandy]], thus diverting the flow of time into an unavoidable destination.

[[WMG: Sassy Cat actually stands for the [[YouCanLeaveYourHatOn Sassy Kat Showclub]]]]
That's why Billy and Irwin love it so much.

[[WMG: Jack's Deal with Death was made to counteract his DealWithTheDevil.]]
* In folklore, Jack got the Devil to agree not to take his soul when he died after scamming him twice.
* One of the solutions on the DealWithTheDevil page is [[LogicBomb to wish for immortality]].

[[WMG: Grim stumbled across "monkey porn" in "The Secret Snake Club"]]
When the Secret Snake Club used Grim to go to Shnissugah's website, before it finished buffering, Grim covers the screen and tells the SSC not to look while the audience hears monkeys screeching and hooting. The mind boggles, doesn't it?

[[WMG: Mandy can tap into the dark forces of the Underworld.]]
Due to being with Grim for so long,Mandy has absorbed the energy of the underworld.Due to her incredible willpower,she has been able to tap into that energy.She used this to overwhelm Grim's magic and control the inhabitants of Endsville.This has also caused her personality to alter from a Jerkass to the AntiChrist
* I don't think Grim had anything to do with it. She had those forces all along..

[[WMG: Mandy became who she is because of Grim's presence.]]
At the beginning of the series, she was just a bratty, cynical, and cunning girl. However, when Grim became their permanent "best friend", she began to grow progressively darker, the true start of her descent being the episode when they peer into the crystal ball, and she sees a future ruled by her. This gave her a lust for power, and began to shape her mind to be fit for an omnipresent dictator she now aspires to be - although she may have gotten a [[IncrediblyLamePun taste]] for it in the first episode.
In a similar vein, Billy's increased idiocity (going from an immature, happy-go-lucky, BookDumb kid to a ChaoticStupid, borderline-psychotic, irritating moron) is also a result of this. Same goes for his father (from a BookDumb slacker quite capable by himself (with a military history) to a immature ManChild).
Grim himself, however, became increasingly more whiny and pathetic as the series went on. Clearly, his continued residence in the mortal world has created an imbalance that resulted in the real world becoming more twisted and supernatural (Irwin's mummy-vampire heritage being revealed, the Goddess of Chaos walking among the mortals, etc.). Meanwhile, Grim himself is leaking (or being drained of) the [[TheSacredDarkness dark powers]] that made the Underworld so otherworldly, making it more demented and corrupt, rather than scary.

[[WMG: Billy is ObfuscatingStupidity.]]
The truth is Billy is the most intelligent person in the universe. He simply has to contain it as it would cause reality itself to distort around him
* Alternatively, he realises that Mandy is the AntiChrist-so he pretends to be utterly stupid in order to ensure he can take down Mandy without her knowing.

[[WMG: In "My Fair Mandy", reality was broken by Mandy ''forcing'' a smile.]]
Mandy has been seen to smile other times in the series, without the same consequence. Notably her true, non-evil smile in the episode "Crushed", where she falls in love. Reality fell apart not because she smiled, but because she ''forced'' a smile. (Also, in the Christmas episode, Grim and Count von Goulash held her mouth open in a smile, so perhaps that didn't count because ''she'' wasn't forcing it?)
* Good point. I never thought of that.

[[WMG: Nergal is [[Franchise/TheSlenderManMythos Slender Man]].]]
My first thought when I first heard about Slenderman. Nergal is a lanky humanoid creature in a suit, with retractable tentacles who kidnaps children. Can't be a coincidence.
* But what if Slenderman is a Nergal?

[[WMG: Grim will eventually kill off Billy and Mandy]]
Think about it - sure, the deal was that Grim would be Billy and Mandy's "friend" forever, but he never promised them immortality, right? At least as far as I know anyway. I think he's just faking being stuck with them, and there's probably some '''massive''' backstory concerning Mandy being such a KarmaHoudini. One day, Grim will kill Billy, and Mandy will try to avoid him, but he'll catch up eventually, and then [[KarmicDeath turn the tables on her]]. He might even throw in an IronicHell, putting her in a similar situation to that episode with the mask (forget what it was though). [[note]]It was the episode where she had to be nice to everyone, otherwise she'd turn into a beast.[[/note]]
* I think it's the inverse-Grim is forced to keep them alive, to ensure they are "friends forever." Of course, that may give him [[AgeWithoutYouth the revenge]] [[AndIMustScream he wants.]] All he needs is patience.

[[WMG: Mandy is the Anti-Christ!]]
It is really obvious only something as evil and wickedly wicked could be the father of Mandy. The Devil had naughty-love with Mandy's Mom, possibly disguised as Mandy's supposed dad, and impregnated her with Mandy. She already became president of Earth during the Underfist special, it's only a matter of time she gets to (or above) her father's level!
* Just to continue on this, Mandy will either [[TheStarscream usurp her father's position,]] an act the Devil will be proud of. After taking over the universe and turning it into Mordor, she will plot [[MultiversalConqueror to take over Cartoon Network.]] She will be stopped by Billy, who is TheChosenZero. And it will be purely by accident.
** So, Billy is the Second Coming?
*** Maybe...At least, the Cartoon Network mulitverse' version of it.
* This means she's the daughter of Him, who is the official Satan of Creator/CartoonNetwork. Yeah, I know about [[WesternAnimation/JimmyTwoShoes Lucius]], but Lucifer and Satan aren't necessasarily the same people.
** Lucius is on a Disney XD show though.......
* There's a big clue with her looks-her hair is shaped like horns. [[{{Satan}} Who else is described]] [[BigRedDevil with having horns?]]

[[WMG:Mandy is Rose Lalonde.]]
From Webcomic/{{Homestuck}}. Both are incredibly smart, blonde, and have a love of all things evil. Their associated colours are both pink and they have very similar haircuts. The events of "The Prank Call of Cthulu" inspired her to research {{Eldritch Abomination}}s. Her mom hid behind a veil of ObfuscatingStupidity and changed Mandy's name to Rose when they left Endsville. Living alone, she learned how to like people (and thus became friends with John, Dave and Jade).
* Plus, both of them have/are close to cats (Mandy's constantly around Milkshakes and Rose has Jasper.) Maybe after moving, Mandy got a cat to remind her of Endsville and Billy.

[[WMG:"Keeper of the Reaper" was one big analogy for/TakeThat at the American Supreme Court.]]
* Okay, bear with me here... Fred Fredburger represents the U.S. Constitution as it applies to American law: he's often vague, typically unhelpful, and just about nigh-incomprehensible to everyone. And yet, the trial ends up hinging on ''him''. Here's where the fun part comes in: all throughout the episode, the judge is driven bonkers by Fred's antics, but when the time comes to declare a verdict, he finally realizes that ''he can "interpret" Fred's nonsense to mean whatever the hell he wants it to mean, and no one can challenge him''. The Founding Fathers, after all, ''intended'' for the Constitution to be as flexible as humanly possible, so that all the competing political parties could use it to their advantage. Luckily for all parties involved in ''this'' case, the stakes were small - the judge just wanted the damn trial to end as quickly as possible (and never see Billy & Mandy again).
** New favourite WMG right here.

[[WMG: [[ButtMonkey Irwin]] is a minor HumanoidAbomination.]]
Let's think about it: his grandfather is Dracula. That's odd enough, but at least Dracula is capable of breeding. His mother, on the other hand, ''is a mummy.'' By all rights, an undead Egyptian should ''not'' be able to bear a child. My theory is that, in order to have a child, they used a TomeOfEldritchLore to defy the laws of nature, and as a result Irwin is [[EldritchAbomination fundamentally wrong.]] However, since it was just a child, it isn't as dangerous as, say, Cthulhu. The reason he continues to harass Mandy is due to the fact she harnesses Grim, and also seems to be wrong at some level. Since the universe dislikes abomination incursions, Irwin is a ButtMonkey ala [[WesternAnimation/SouthPark Kenny.]] He doesn't [[TheyKilledKenny die a lot]] because [[spoiler:Kenny is related to Cthulhu, instead of just being brought into being by Lovecraftian magic.]]

* Well, if the mummy is still somewhat alive, [[{{Squick}}maybe the ovaries still work but just have really gross eggs in them.]]
* Dick's father is Dracula, which makes him a [[{{Dhampyr}} Dhampyr]], and since it makes him a half-monster, and mummies are monsters then that explains the compatibility, of course we don't know this until "Dracula Must Die!"

[[WMG:Mandy is the daughter of Him and Eris]]
It was a dare by the Red Guy. When Eris realized she was having a child, she switched the baby with a random one at the hospital, which happened to be Claire and Phillip's. And since Mandy is the daughter of the goddess of discord and the lord of the underworld, monsters and supernatural beings are attracked to her like Billy to pie. Plus, the wolves actually wanted to kill her, they lied.

[[WMG:''Billy and Mandy'' is a prequel to ''WesternAnimation/AdventureTime'']]
According to the ''Adventure Time'' episode "Son of Mars", Abraham Lincoln used to be immortal, but gave up his immortality and traveled back in time to be killed by John Wilkes Booth. In ''Billy and Mandy'', he's inexplicably still alive and appears to still be President. Clearly, ''Billy and Mandy'' is set in the timeline before Lincoln allowed himself to be killed in the past. The many supernatural forces in the show were partially responsible for how post-Mushroom War Earth became so bizarre.
* Why is Death so different and seems to be free from Billy and Mandy? Mandy realised she could never [[OmnicidalManiac be alone]] since Grimm would make DeathIsCheap because of the deal to "be friends forever." Solution-cancel the deal, and so that Grimm didn't get suspicious he'd give her some of his powers. Grimm decided to go back to death metal and get some street cred, leading him to once again be a respected figure. Billy had his last wish be for some hot dogs to come to life, which is why [[TooDumbToLive the Hot Dog Knights are so unbelievable stupid.]] Mandy designed the Mushroom Bomb, using her new death-based powers and iron will to give it strength, and gave it her hatred towards all life. [[spoiler:The Lich was so successful [[GoneHorriblyRight even Mandy couldn't control it.]] ]]

[[WMG: Billy isn't stupid]]
Billy really is as smart as his father says. In fact he was so smart that he threatened to upstage Mandy so she, being the {{Enfante Terrible}} that she is, did something horrible to him that turned him into a nose-picking scatterbrain. Mandy knows that if Billy were to ever repossess his intelligence, he would wreak horrible retribution against her. As a result, no matter how annoying he is now, she must keep him around her at all times so she can keep her eyes on him if there ever comes the possibility of him reverting back to his old self.

* If one takes into consideration [[https://www.youtube.com/watch?v=vVTyJ3Yecx0 the old short that Maxwell Atoms made in college]] starring Billy and Mandy... This theory just might be canon.

[[WMG: Grim has a Jamaican accent because his Granny and Great Aunt Kali practically raised him]]
I mean, think about it. As far as we know, Grim, his Granny, and his Great Aunt Kali, are the ''only'' ones in his family that have Jamaican accents. His mother sounds Jewish, and his Father is pretty much [[Series/That70sShow Red Forman]] in skeleton form, so Grim couldn't possibly have gotten his accent from his parents.

* Maybe Grim's parents went out a LOT when he was growing up, either for work or just dinner dates, so they'd just leave him at either his Granny's or Great Aunt Kali's house for them to babysit him. And, since their voices were the main ones he heard when he was finally learning to talk, it lead to him developing a Jamaican accent as a result.

[[WMG: Billy's real father is a Sasquatch]]
In the episode, "Bearded Billy", when Billy takes one of Grim's potions to increase his hair growth, he ends up covered completely in hair. When Gladys sees him, she goes into a rampage, saying that she told him "it was over" and that there was an "agreement that he'd never return" and then calls him a "stalker Sasquatch". At some point in the past, Gladys must have been romantically involved with a sasquatch who got her pregnant with Billy. She was worried about Harold finding out about the affair, but luckily, Billy was born looking completely human and so she was safe, but she ordered the sasquatch lover to go back where he came from in order to protect her and Billy. When Billy took the hair growth tonic, his look became easily like his biological father.

[[WMG: Irwin is actually [[StepfordSmiler secretly depressed]].]]
A lot of insane crap happens in Endsville, and [[TheChewToy Irwin has some (if not most) of the worst luck of all the characters]]. Other characters who are like him react appropriately: Grim always complains about Billy and Mandy, Junior is melancholic and desperate for friendship, and Pud'n' cries a lot and is in a constant state of caution. Irwin, on the other hand, only gets upset when bad stuff is actively happening; otherwise, he seems fine. But really, that doesn't make much sense looking at the other characters. He's probably hiding some serious depression from everyone else.
** Maybe his mummy/vampire heritage allows him to be stronger willed than the others.

[[WMG:The wolves Pud'n was raised by are the same ones who tried to claim Mandy when she was born]]
Mandy's parents said no, so they settled for Pud'n instead.