[[WMG: Griffin is a InvisibleStreaker.]]
Wayne pulled down Griffin's swimming trunks, and he wasn't wearing anything underneath. This theory is plausible.
* Creator/HGWells' [[Literature/TheInvisibleMan book]] states that Griffin's clothes aren't invisible.
* He'd be older than Mavis because he's the same Griffin; the serum made him immortal.
** Except the original Griffin was an albino, and the HT version insists he's a redhead. Possibly the serum's effects messed with its inventor's genes so invisibility became hereditary, and this version's his great-grandson?
* As a side note, in the book, Griffin turned a piece of white cloth invisible, his sciency stuff just got destroyed before he could make invisible clothing. Since it's been about a hundred years now, he's probably had enough time to re-create his invisible-making machine. So he may be wearing invisible clothing most of the time, he'd be cold without it. So as for the swimsuit, it may be visible due to personal choice (he happens to like that particular pair and wants them to remain visible). As for the glasses, making them invisible might interfere with his eyesight somehow.

[[WMG: Jonathan has ADD/ADHD.]]
Have you SEEN the way he acts?

[[WMG: Jonathan probably had a girlfriend named Mina.]]
If there's a sequel (and if this weekend's opening numbers are any indication, there most likely will be), she will come looking for him and try hunting down Dracula and Mavis, making her the film's main antagonist. She'd probably be the girl that was "just a fling" that Jonathan mentions in the song at the end.

[[WMG: Possible plot synopsis' for a sequel are...]]
* Knowing that some humans are actually okay with the existence of monsters, Drac allows humans to come to the hotel as some sort of Visit Transylvania tour.
** A vampire/monster hunter would arrive as a guest, bent on taking down Dracula. Probably Van Helsing.
* Jonathan and Mavis return from their travels and announce that they are getting married.
** Meanwhile, they have to deal with the fact that Mavis can't survive in daylight and that [[MayflyDecemberRomance Jonathan will probably grow old and die while Mavis is still the vampire equivalent of a young adult]]. Especially because "you can only zing once". This will probably result in Jonathan becoming a vampire. Which he will think is "totally cool!"
* The monsters will need to meet Jonathan's parents and get accustomed to the world outside, a la ''Shrek 2''.
* In a side story, Dr. Victor Frankenstein, now extremely old, has finally tracked down Frank and is determined to dismantle him for good.
* Horror villains from today's horror movies who ''are'' extremely scary, like creepy children, [[TheRing a girl crawling out of a well]], dolls, chainsaw serial killers, or even Slenderman, battle with the classic monsters.
** Once the main characters get over how terrifying they are, they'll realize that while those guys may be dangerous to humans, against [[VoluntaryShapeshifting Wolfman]], [[MightyGlacier Frankenstein's Monster]], [[SealedEvilInACan a mummy]], [[{{Invisibility}} the Invisible Man]], and [[BadassCape lord of the vampires himself]], they wouldn't have such luck.
*** ...And they would ''still'' prove they can be [[EvilerThanThou Scarier Than Thou]]!
*** Meanwhile, Jonathan will have outgrown his TooDumbToLive status (maybe [[RescuedFromTheScrappyHeap rescuing him from the Scrappy heap]]) and will be MrExposition for the older monsters. He will [[BrokeYourArmPunchingOutCthulhu nearly be killed trying to help]] and Mavis will have to perform an EmergencyTransformation on him.
* A prequel explaing how the the five main monsters meet and how Dracula is related to Frankenstein.
** Jossed by Selena Gomez (Mavis Dracula's voice actress), who confirmed that she's recording alongside Andy Samberg (Jonathan's voice actor). This all but confirms that Hotel Transylvania 2 will be a sequel, not a prequel.
** [[HonoraryUncle I assume Mavis calling him "uncle" is out of friendship]]. I don't think he's actually related to the vampires.
** It's entirely plausible that he really is her uncle in the sense that relations seem to work with Frankensteins/Prometheans/Patchwork Creatures/Whatever. Frankenstein seemed to buy the "related to his hand" story, suggesting that's really how that works, or else Frankenstein is just a colossal idiot, which he only shows minor signs of. If it doesn't require human parts to make a Frankenstein, then it's entirely possible that Frankenstein has one or more bodyparts from one of either Dracula or Martha's siblings.
* A prequel covering the actual construction of the hotel. Could also shed more light on Dracula's marriage and backstory.
** Jossed by Selena Gomez (Mavis Dracula's voice actress), who confirmed that she's recording alongside Andy Samberg (Jonathan's voice actor). This all but confirms that ''Hotel Transylvania 2'' will be a sequel, not a prequel.
* A prequel covering Jonathan's childhood.
** Jossed by Selena Gomez (Mavis Dracula's voice actress), who confirmed that she's recording alongside Andy Samberg (Jonathan's voice actor). This all but confirms that Hotel Transylvania 2 will be a sequel, not a prequel.
* Jonathan brings his family to the hotel, not knowing that his family is an ancient order of monster hunters. HilarityEnsues.
* Going to the ruins where Martha was burned. After all Jonathan did say he felt a spirit there.
** He is a Seventh Son, after all. Perhaps he was able to feel Martha's spirit there as a result.
* Humans and mosters will be living in harmony... for the most part.

[[WMG: Mavis may not share her dad's garlic allergy.]]
There's just something about the expression on her face when she asks "is that garlic" that makes her seem excited. Or perhaps she doesn't know she's allergic. Maybe she found out. She sounds upset when she's telling him about it later: "It was horrible! They had garlic on bread!" More likely the excitement on her face is really surprise, as she's probably never seen garlic bread before.

[[WMG: Vampires grow to look progressively less human as time goes on]]
Asides from fangs, Mavis looks like a completely normal girl. Drac also looks human, but his ears, unlike his daughter's, are pointed. Grandpa Vlad, probably very ancient, looks utterly monstrous in comparison. If given enough time, his son and granddaughter will likely appear more inhuman in the same way.

[[WMG: Jonathan is [[MagicalSeventhSon the seventh son of a seventh son]].]]
He briefly mentioned that he has six brothers, and that's a pretty big hint right there. He discovered the hotel, not out of curiosity and dumb luck, but because he was magically drawn to it.
* To confirm this, of course, it'd need to be confirmed that they were six ''older'' brothers. If not, maybe his ''younger'' brother could turn out to have PsychicPowers.

[[WMG: Quasimodo is a [[OurGhoulsAreCreepier ghoul]].]]
He looks creepy, is possibly 600 years old, and wants to eat Jonathan.
* Alternatively, Quasimodo is a LegacyCharacter. He's not the real Literature/{{Hunchback of Notre Dame}}, but a ghoul who was named after him. He took the logical consequence of this by naming his pet Esmeralda. This seems to be supported by one of the knights saying "Quasimodo Wilson, you are coming with us." His last name's Wilson.

[[WMG: Quasimodo was brought BackFromTheDead as something NotQuiteHuman]]
Probably something closer to, ironically, a gargoyle.

Most likely something to do with how during his life he still risked his life to protect another (he probably named his rat in memory of her) and was given a second chance. Unfortunately, since he's part gargoyle, he now has a taste for human.

[[WMG: Dracula's wife was human.]]
The backstory seems to suggest this. The mob killed [[CategoryTraitor her just for]] [[MalignedMixedMarriage marrying a monster]], or they believed she was a vampire herself or probably a witch. Another reason why Dracula didn't want Jonathan around Mavis. That would make Mavis a dhampir (related to the theory above about not being allergic to garlic, since she might only have a few vampire weakness).
* On the other hand, her gift to Mavis includes a story about the meeting saying they were two bats who bumped into each other. While this doesn't fully rule out the possibility of this WMG, it does throw some serious doubt on it.
* Confirmed to have been originally planned, but was changed when Gennedy Tartakovsky became the director. According to commercial artist Marcelo Vignali, who worked on the concept art in 2008 for Mavis's bedroom with original director Jill Culton, "In Jill's version of the story...[Mavis] was half human -- only she (Mavis) didn't know it! Mavis wondered why she couldn't turn herself into a bat, or when her fangs would finally grow-in. Dracula just explained to her that she was simply a late-bloomer -- concealing the fact that Mavis' mother was human." Vignali also writes on his website, "...In Jill's version of the story, Dracula was still the over-bearing and controlling father as he is in the final version of the story that made it into theaters. But, in this version, Dracula had intimidated all the other monsters in the hotel to play along and convince Mavis she was simply a late bloomer. His fear was that would discover she was human, and leave the hotel. When the Johnathan-character (love interest) arrives at the hotel, Mavis soon discovers that she isn't a monster, and that she's been lied to all this time." When Tartakovsky took over the directing helm from Jill Culton, Mavis's half-human side was scrapped, and she was written as a full vampire instead. According to Wikipedia, "In less than a year [2011-2012], Tartakovsky rewrote the script [for Hotel Transylvania] and reimagined the film to follow the energy, organicity and exaggeration of 2D animation, particularly as seen in the work of director Tex Avery."
** [[spoiler: Some of this plotline would later be used in ''WesternAnimation/HotelTransylvania2'', with the concern over Dennis being fully human or a merely a "late-fanger" and maybe leaving the hotel.]]

[[WMG: The Invisible Man's glasses are magic.]]
And I don't mean because [[ExpressiveMask they warp about]] [[EyeGlasses to show his expression]]. See, for the Invisible Man to ''be'' invisible, light would have to pass through him completely - eyes included. But because light passes straight through his eyes, and therefore his retinas, he ought to be completely blind. At least without a pair of magic glasses allowing him to see. (Granted, the fact that he's able to kick Drac's ass while trolling him in the beginning ''without'' them on puts a hole through this theory, but still.)
** Alternately they're just normal glasses because MST3kMantra.

[[WMG: Dracula will obtain a SecondLove in the sequel.]]
She will be human and Mavis will play matchmaker all the while saying "I told you so."
* Since "you only zing once", chances are that if Dracula does find a SecondLove, [[ReincarnationRomance she'll be the reincarnation of his dead wife, Martha]].
** Jossed for the sequel.

[[WMG: Franchise/ThePhantomOfTheOpera was one of the architects for the hotel]]
Just look at the tunnels Dracula goes through. As with Quasimodo and the Invisible Man, he's close enough to be considered a monster.
* He does show up in the sequel...

[[WMG: Vampires in this movie's universe are not immortal, just LongLived]]
Everything suggests that Vampires go through the same stages of life as humans, just much slower. They are born as babies, then age through childhood and puberty untill they reach adulthood, and as proven by Dracula's father they eventually grow old. No relatives of Dracula older than his dad are ever seen, so they most likely eventually die of old age. It just takes many centuries for them to get to that stage.