Archive of Our Own

This is a list of common differences between canon and fanon. I have created it primarily to keep track of which is which, since I often have difficulty distinguishing between them in my own work. I've tried to keep it factual, well sourced, and neutrally worded.

Please bear in mind that every version of a work of fiction is equally true (i.e. they're all 100% false). Canon is not "superior" to fanon. But it is important that we keep track of where different ideas came from, so that we do not become unduly attached to ideas which do not fit our particular conception of the Undertale mythology.

Sans

Sans is one of the more popular characters in the fandom, if not the most popular, but he's also one of the most divisive. Interpretations of him vary substantially, so this list will not attempt to catalogue every possible misinterpretation of canon. Instead, we'll focus on a few of the more popular ones.

Alcohol

• Fanon: Sans is an alcoholic.
• Canon: Alcohol probably works on monsters (source: the bunny monster in the lower right corner of Grillby's looks and acts drunk), but there's no evidence that Sans ever drinks any. He is consistently alert and lucid enough that intoxication can probably be ruled out. If he has any dietary problem at all, an eating disorder is more plausible (source: Papyrus's dialog regarding Sans and Grillby's suggests the former is primarily going there to eat, not drink).

Depression

• Fanon: Sans is depressed, which means he cries a lot, is a nervous wreck, and generally acts like an emo 14-year-old.
• Canon: Sans is depressed, which means he sees no point in doing anything, is withdrawn and passive, and Papyrus mistakes all of this for "laziness." (Source: Some of the dialog in his boss fight is suggestive of this, but the rest is conjecture.) Admittedly, "depression" might not be quite the right word for what's going on in Sans's head, but some of its common symptoms are fairly close to Sans's apparent behavior.

Grillby's

• Fanon: Sans's bar tab is huge and unpaid.
• Canon: There is no evidence of this. Papyrus does say that Sans spends a lot of time at Grillby's, but that doesn't mean he's in arrears.

Papyrus

• Fanon: Sans is extremely protective of Papyrus, and can't bear the thought of anyone hurting him.
• Canon: Less clear. If Frisk kills Papyrus, Sans does not appear in the game again until the Last Corridor (except for one brief mention), by which point he has clearly gotten his emotions under control. We could read this as Sans shutting down after his brother dies, or we could just as easily read it as him shunning Frisk for the murder of his brother. On the other hand, Sans does lie to Papyrus in several of the Neutral Route endings, apparently to protect his feelings. Sans obviously cares about Papyrus a great deal, but depictions of him completely shutting down after Papyrus dies are an interpretation of limited evidence.
• His appearance during Shyren's concert is even more baffling. If he's really non-functional, he probably wouldn't be following Frisk around, but on the other hand, why follow if not to confront? He also fails to appear in several social locations such as Grillby's, which might be indicative of withdrawal. This is further complicated by his possible depression.

Puns

• Fanon: Sans tells a lot of puns.
• Canon: Sans tells a lot of jokes of many different varieties. He does make several puns while Frisk is hiding behind the conveniently-shaped lamp. In the rest of the game, he draws from many different types of humor, including a few puns here and there, but also physical comedy (multiple whoopee cushions, the stack of hot dogs), knock-knock jokes (with Toriel), double entendres ("you really like hot animals, don't you?"), verbal irony ("i mean, look at yourself. you haven't died a single time."), etc.

RESETs

• Fanon: Sans can remember RESETs.
• Fanon: Sans cannot remember RESETs.
• Fanon: Sans cannot remember RESETs, but something in his workshop can.
• Canon: Unclear. Sans is definitely aware of RESETs, the turn system, and (probably) that Frisk is the anomaly, right from the start (source: dialog in his boss fight). His dialog during the Grillby's "date" suggests he is unaware of Flowey's true nature, but he might not sufficiently trust Frisk at that point in the story. Even during his boss fight, he continues to claim that he is reading Frisk's facial expressions and not actually remembering past RESETs. It seems implausible that he's shortcutting back to his workshop to take notes every time the player dies to him and RESETs, but it also seems implausible that he would continue to lie about this while being truthful about everything else.
• Unfortunately, there is a further wrinkle. Nearly all of the evidence under this heading is based on Sans's dialog. But Sans has a demonstrated history of trying to manipulate the player, across both Undertale (his boss battle) and Deltarune (he pretends to already know Kris). If Sans is not a reliable source of information, then we may have to discount all of that evidence, and conclude instead that we know nothing about Sans, or his capabilities.

Chara and Frisk

We know so little about these characters that any depiction of either of them will inevitably turn into a de facto OC. Since I don't really have any canon evidence to work with, I won't be comparing against canon here. Instead, I will focus exclusively on common fanon differences between the two of them. There are no sources given for this section of the list because it is entirely based on fanon.

Abuse

• Chara: Physically or psychologically abused, actively, over an extended period.
• Frisk: Abandoned, neglected, or psychologically abused, often (in the latter case) less severely than Chara.

Biological family

• Chara: Usually cult-ish or reclusive, sometimes wealthy.
• Frisk: Usually poor or dysfunctional, sometimes deceased.

Personality

• Chara: Nihilistic, often vengeful. Sometimes evil or of ambiguous morality. Usually has trust issues.
• Frisk: Existential, pacifistic. Often has abandonment issues. Sometimes has trust issues, especially if the No Mercy run has been completed.

The other humans

Again, we know almost nothing of these humans, so this is a list of stuff we don't know.

Age

• Fanon: 8-12
• Canon: Indeterminate. Toriel's guest room has shoes of various sizes as well as toys, but it's not clear if she would have given an adult anything special.

Gender

• Fanon: Cyan, Blue, and Green are usually female. Orange and Purple are usually male. Yellow used to be usually male, but a popular fan game depicted Yellow as female, and now it's unclear which is more popular. Some fans depict all six as gender neutral or non-binary. Those stories usually do the same for Chara and Frisk.
• Canon: We don't know. Statistically, all eight humans being non-binary is unlikely but not impossible.

Manner of death

• Fanon: Asgore personally killed them all.
• Fanon: Cyan died in the ruins, being unable to move. Orange died in Snowdin, being unable to hold still. Blue died in Waterfall, because the attacks in that area are hard to dodge at the bottom of the bullet box. Purple made it further into Waterfall, but was unable to properly fight Undyne, and died there. Green was felled somewhere in Hotland, possibly by Muffet, when a monster attacked the center of the board from multiple directions at once. And Yellow made it all the way to Mettaton or possibly Asgore.
• Canon: Asgore never explicitly says he killed them. He certainly called for their deaths and instructed his people to kill them (source: Undyne's spiel, New Home, and some of Papyrus's dialog). But you find their stuff scattered across the Underground.

Order

• Fanon: Cyan, Orange, Blue, Purple, Green, Yellow.
• Canon: This is the order in which you find their stuff, and the order in which they appear during the Omega Flowey battle. But it's not necessarily the order in which they fell down in the first place.
• However, from a thematic perspective, it makes more sense to have a single order than to have two or three different orders, so it's not an unreasonable interpretive choice.

Papyrus

On the other hand, we know a great deal about Papyrus thanks to his date and the cell phone. So, without further ado:

Age

• Fanon: Younger than Sans (usually).
• Canon: Surprisingly, the Japanese localization confirms this. Japanese has separate words for "older brother" and "younger brother," so at least in that localization, Papyrus is unambiguously the younger brother.

Favorite food

• Fanon: Spaghetti
• Canon: Not spaghetti. Possibly "that oatmeal with the dinosaur eggs", if you believe Flowey.

Intelligence

• Fanon: Papyrus is an idiot.
• Fanon: Papyrus is secretly a genius, and just acts like an idiot.
• Canon: In at least one neutral ending, Sans is able to maintain the charade that most of the other major characters are "on vacation," after Frisk killed them. However, in the same conversation, Papyrus does display some signs of self-awareness, and knows that things are worse than they seem. He keeps this information from Sans, presumably because he does not want him to worry.

Jokes

• Fanon: Papyrus hates jokes of all kinds, or puns specifically. If he makes a pun accidentally, he freezes up in horror.
• Canon: Papyrus makes a pun during the conveniently-shaped lamp scene, right after Sans's second rimshot. It's very obviously deliberate. He is probably retaliating against Sans, but he's still willing to use puns to fight puns. Also, a lot of his other dialog contains jokes of various kinds, usually when Sans is absent.

Strength

• Fanon: Papyrus is a noncombatant, and is incapable of seriously fighting anyone.
• Canon: Undyne describes him as "really freaking tough" during her date, but she admits that he lacks the mental discipline to be a warrior.

Flowey

And Asriel, too.

Asriel

• Fanon: Flowey hates being called "Asriel" and thinks of himself as a different person.
• Canon: We don't know. Asriel mentions that he would prefer for Frisk to think of him "like this" rather than as Flowey. But it's not clear that they are actually distinct personalities. During his boss battle, he says he was "tired of being a flower," and in the No Mercy route, he describes reaching out to his parents in an earlier timeline. The line in the Ruins could be an expression of guilt or regret.
• On the other hand, it's fairly obvious that Asriel dislikes his time as Flowey. But this need not be reciprocal.

Feelings

• Fanon: Flowey is incapable of feeling love or compassion.
• Canon: Asriel reports that, as Flowey, he never experienced those emotions, and he also says this as Flowey in New Home. He does claim that he is categorically incapable of those feelings, but it's unclear whether he extrapolated this from his personal experience, or from reading up on SOUL science. If the former, he might be mistaken.
• If he were human, he would have been suffering from some variety of PTSD and probably other effects, and to the best of our knowledge, he never received any kind of professional treatment for those conditions. It also stands to reason that the time loop would have made matters worse. Some of his dialog in New Home is suggestive of survivor's guilt, which seems quite odd if he can't feel love in the first place. Ultimately, this is a matter of conjecture and interpretation.
• Having said that, a categorical incapability is probably the most straightforward interpretation of the available evidence.

Floweypot AU

• Fanon: Potted!Flowey is kind of a jerk. In some iterations, he's murderous, while others portray him as indifferent to everyone.
• Canon: Again, it's not clear. After the credits, Flowey implores the player not to RESET, and to let Frisk have their happy ending. It certainly seems like he's changed for the better. We also know that he spent a lot of time trying to help people before he started killing (source: No Mercy route, New Home dialog). But Asriel previously says that he would have no feelings of love or compassion in that state, so he might relapse, given enough time. For a more thorough discussion of whether Flowey could recover without a SOUL, see No Soul Necessary: Flowey's Happy Ending.

Interactions

• Fanon: Flowey is a master of social engineering. He can manipulate anyone into doing anything.
• Canon: Flowey's attempts at manipulating Frisk and/or the player are transparent and ineffective on the Pacifist and Neutral routes, and nonexistent on the No Mercy route. The player does as he says (after sparing him) because they want to see what happens, not because they seriously believe he is telling the truth. In his New Home dialog, it is implied that Flowey is only good at manipulating people because he thoroughly save-scummed his way through every possible interaction, so he learned it all by trial and error.

Minor encounters

Any encounter who isn't a miniboss or boss. In other words, any monster you can encounter more than once in a single playthrough.

Pronouns

• Fanon: Every monster uses exactly one of he/him, she/her, and they/them.
• Canon (if you assume the narration and all dialog uses correct pronouns): Based on this masterlist, a plurality of monsters exclusively use it/its. The next largest group uses multiple pronouns, all of whom include it/its as one of their pronouns. They/them appears to be relatively unpopular, and usually appears in conjunction with another pronoun.
• If you don't take the narration as correct, then the next-best interpretation is that the narrator (who is probably Chara) is calling some monsters "it" to demean them. This works, because the vast majority of the time, it/its is only used by narration, and not in dialog. Further, several characters are called "it" in the narration and something else in dialog. If you're going for an "evil narra-Chara" interpretation, this fits nicely.
• Interestingly, the distribution of pronouns shows a marked pattern: The most important characters to the plot (Sans, Undyne, etc.) all use binary pronouns. The less important, but still significant characters (Napstablook, Monster Kid) often use they/them, sometimes in conjunction with it (Gyftrot, Mad Dummy). The least important characters, who are basically just filler, are mostly it/its. There are a few characters who break this pattern, such as Aaron and Shyren, as well as a few other pronoun combinations, but it's surprisingly consistent.