- Ambiguous Situation: There are hints throughout the series that he and the timeline he came from are not all they appear to be. X-event Chara blatantly tells him that he knows there is something wrong with him and the main universe in 0.3 part 2.
- Beware the Silly Ones: Just like his canon self.
- Decoy Protagonist: Gets heavily overshadowed by Ink.
- Properly Paranoid: He's suspicious of Ink the first time they meet. And rightfully so.
- Pungeon Master: He loves making them.
- Reluctant Hero: Originally, he didn't even want to join Ink on his adventure, but changed his mind once the half of his soul Cross left him started to cause problems.
- Anti-Hero: Does not particularly like the rest of the cast, but joins them anyways because it's whats "right".
- Berserk Button: Don't tell puns around him. He hates them.
- Dark Is Not Evil: He may not be the nicest looking, but he's on the good guys' side.
- Impaled with Extreme Prejudice: Together with Swap at the end of 0.4.
- Jerkass: Very much so.
- Jerk with a Heart of Gold: After the events of 0.3 Part 2, he is seen comforting Underswap!Sans (who has just lost his home and his brother) in 0.4, showing that while he may not be the nicest, he has a softer side to him.
- Sir Swears-a-Lot: Almost every other word uttered by this version of Sans is a swear.
- Adorkable: This is Underswap Sans we're talking about.
- Break the Cutie: Goes through a terrible one throughout 0.3 and 0.4, watching his brother losing faith completely, having his timeline and everyone in it erased, and having his supposed new friend betray him. To make things even worse, it finally ends with him being killed by XGaster.
- Catchphrase: "Mweh heh heh!"
- Go Out with a Smile: When XGaster impales him, he has a vision of all of his friends still being alive, causing him to invoke this trope.
- He Knows About Timed Hits: Knows to some degree about the problems with Cross.
- Impaled with Extreme Prejudice: Together with Fell at the end of 0.4.
- Kill the Cutie: XGaster kills him and Fell in 0.4.
- Sole Survivor: X-event Chara corrupts and ultimately destroys his entire universe, with only Swap being able to escape with the heroes. Ultimately subverted however, as he dies at the end of the very next episode.
- The Cutie: He's an adorable little ray of sunshine. Until his universe gets destroyed.
- Killed Offscreen: Although the audience doesn't get to see the body or his fight with Killer, he's never seen again after the camera cuts away, and due to Killer being present later on, it's heavily implied that this was his ultimate fate.
- Nice Guy: He welcomed Sans with open arms and was more than willing to help him find Ink, even though they had just met.
- We Hardly Knew Ye: He barely gets any time to talk with Sans before he is killed by Killer.
- Wide-Eyed Idealist: He simply cannot imagine that someone could be greedy enough to consider themselves the owner of a whole universe.
- Arch-Enemy: To Error, who wants to destroy all of the Alternate Universes he has worked to protect.
- Brutal Honesty: Has a habit of just saying whatever he wants without thinking of how other people might be affected by it. This kind of foreshadows his true nature as The Sociopath, though a first-time viewer might just think that he's being Innocently Insensitive.
- Chaotic Neutral: Xtra scene 2 reveals he was never really on either the good guys' or Cross' side. He views the whole situation as a fun game he and XGaster are playing.
- Cloudcuckoolander: He can act very strange, focusing only on Error's new outfit when they were supposed to be having a serious discussion. He also tends to forget what he was talking about in the middle of a sentence. This is later revealed to be an act he puts on, as part of his "game".
- FaceHeel Turn: Pulls this in 0.4.
- Emotion Eater: The colored vials he has on his belt are actually filled with all different emotions. He needs to refill them in order to be able to feel since he doesn't have a soul. It starts to show in 0.3 Part 2 and others start to take notice of it. In 0.4, he's stopped taking them altogether, finishing his slow transformation into an Empty Shell.
- Empty Eyes: After he starts to become emotionless, his eyes change from multi-colored to a dull white, with no visible emotion in them.
- Empty Shell: He officially becomes this in 0.4 after he voluntarily stops taking his emotion vials.
- Evil All Along: He's been working for XGaster the whole time.
- Eviler Than Thou: Pulls this on Error in 0.4 and technically in Xtra Scene 2, though whether or not Error was just Dreaming of Things to Come or if Ink and XGaster were really speaking to him is somewhat left open.
- He Who Must Not Be Seen: He has to make sure that he makes as little contact with the Alternate Universes and their characters as possible so as not to disturb the natural order of things.
- Moral Event Horizon: In 0.4, he full-on turns on his own team, letting XGaster murder them in cold blood.
- Motive Decay: As the guardian of all AUs, he originally just wanted to protect other people's creations. However, as more and more creators started to abandon their works, the Doodle Sphere slowly collapsed in on itself and he became terrified of eventually being forgotten along with it. After he met X!Gaster and the latter promised to him to help him feel even without having to rely on the creation of new worlds, he seemingly abandoned his duties altogether, due to a desire to finally experience something new.
- Mr. Imagination: All of his attacks are based around Ink's creative mind.
- The Dragon: To XGaster as of 0.4.
- The Sociopath: Arguably even more so than XGaster. While XGasters' eventual Lack of Empathy came about as a result of him going Drunk with Power due to the reality altering capabilities of the Overwrite button, Inks' comes from him having no soul and having to rely on artificial emotions to function.
- Took a Level in Badass: After he stops taking his emotion vials in 0.4, he's able to effortlessly hammer Error into the ground.
- Took a Level in Jerkass: And how! After he becomes an Empty Shell in 0.3, his demeanor changes from cheerful and kind to cold, distant, and ruthless. He denies that Sans, Swap, and Fell are his friends, frees XGaster even though he knows how dangerous the latter is, and even flat-out admits that he does not care for the multiverse and that the only thing he truly cares about is being able to feel when a new universe is created.
- Pet the Dog: In hindsight, him coming back to X-Tale and befriending Cross was this. He had no reason to check up on Cross, since by that point he was already in possession of half of X!Gasters soul. In fact, considering X-Event Charas status as Cross's Enemy Within it was actually a huge risk on his part.
- Unwitting Instigator of Doom: He was the one who originally showed X!Gaster the Multiverse, in an attempt to re-inspire him and keep him from destroying his world. It worked a little too well. XGaster, upon seeing all of the different pacifist timelines, became obsessed with creating the perfect world, which led to him starting the X-Event experiment. Somewhat zig-zagged, as he's revealed to have been working for XGaster the whole time, despite knowing what he did.
- Using You All Along: He's been doing exactly this to the entire cast from the very beginning. He never truly cared about what happened to them or their homes. He merely needed them for his and XGaster's "game".
- Vomit Indiscretion Shot: Whenever he gets especially worked up about something he starts to vomit black ink.
- What Measure Is a Non-Unique?: He firmly believes that destroying or ruining a small fraction of the Multiverse doesn't matter since there are at least thousands of Alternate Timelines per Alternate Universe. As such, he sees the worlds of his "friends" as nothing more than expendable little blips on a much larger scale.
- The Archer: While he does use a bow as his primary weapon, Dream himself is a complete subversion of the usual archetype: he's a kind All-Loving Hero who tends to get overly emotional and clearly has a lot of respect for Ink.
- Allergic to Evil: He can't use his powers in a negative environment. (I.E, no one can be happy in a certain situation.)
- Crippling Overspecialization: His powers only work when at least one person close to him feels positive feelings/has happy memories and even then his skill-set seems to be limited to teleportation and his bow.
- Energy Bow: The arrows he shoots are made of positive feelings.
- The Empath: Like his brother, Dream can sense emotions. He works to preserve/engender positive ones.
- Good Is Not Soft: He is able to take down Nightmare in seconds with just a few shots from his bow when previously the combined powers of Classic Sans, Underfell Sans, Underswap Sans and Underswap Papyrus weren't able to put a scratch on him.
- Light Is Good: Played straight.
- Sacred Bow and Arrows: His bow is the only weapon that can actually hurt Nightmare - because the arrows he shoots from it are made out of positive feelings, Nightmares' Kryptonite Factor.
The main antagonist of Underverse. An alternate version of Sans that is the only survivor of his world after a Genocide run without reset capabilities... or so he thinks.
- Big Bad Wannabe: He tries really hard to make himself out as a threat, but the poor guy has to either rely on others for his plan or get the Eviler Than Thou treatment from his supposed "allies" who constantly trick and use him.
- Embarrassing Nickname: He actually hates being called Cross and would rather people just call him Sans. "Cross" was the nickname X-event Frisk gave him in the very timeline he tried to kill him in.
- Genocide from the Inside: In the prequel comic it's revealed that Cross himself was the one who murdered nearly everybody in his world during a misguided attempt to become the new X-event and claim the OVERWRITE-button for himself. It ultimately failed, due to Cross' being a monster and thus unable to actually use the button.
- Neutral Evil: To Chara's Chaotic Evil.
- Red Oni, Blue Oni: The Red Oni to Chara's Blue Oni.
- HeelFace Turn: The end credits scenes of 0.4 imply he will go through one.
- Hybrid Power: Has most of his "Sans" attacks while also being able to use knives thanks to the human half of his soul. That is, until Cross is finally separated from him in 0.4.
- Tragic Villain: He genuinely doesn't want to harm anyone, he just wants to rebuild his home.
- The prequel comic expands on this. Cross was simply a royal guard in charge of protecting X-Event!Frisk alongside his brother. He had no idea about the secret war for the Universe or that his own code was being manipulated. He then attempts to become the X-Event himself by absorbing X-Event!Frisk's soul after seeing his true nature. In doing so, he not only ensured the destruction of his home, but also lost any chance of being able to OVERWRITE due to his status as a monster locking him out of using the OVERWRITE button. No wonder he wants to rebuild his world so badly.
- Sanity Slippage: In the prequel comic. Granted, he was slowly dying at the time and everyone, including his own brother, had just tried to kill him. It really shines through during the final fight against all of them.
- Scars Are Forever: His trademark red scar. Not even a RESET can take it away. Subverted in 0.4 when XGaster revives him. He no longer has the scar as a result.
- Well-Intentioned Extremist: He will do anything to rebuild his home.
- He attempted to steal X-Event!Frisk's SOUL because, as XGaster had pointed out, there was nothing stopping them from becoming just like him eventually, and their manipulations up to that point certainly did not make them look good.
- Woobie, Destroyer of Worlds: He's lost everything thanks to XGaster and X-Event!Frisk's on-going fight for their universe. All he wants is his friends and world back.
- All for Nothing: X!Gaster's restoration in 0.4 renders everything he'd worked for in the season meaningless. When it sinks in, he's not too happy about it.
- Antagonistic Offspring: Thanks to a combination of his father's perfectionist attitude and the X-Event experiment, he's very upset with him and actively revolts against him with his brother in the prequel comic.
- Badass in Distress: 0.4 sees him completely at the mercy of Nightmare and Killer. At one point, he's seen trying desperately to keep them from force-feeding him a monster-soul.
- He's taken captive by XGaster at the end of the episode.
- Big-Bad Ensemble: He's The Man Behind the Man for Cross, then becomes The Heavy for the rest of the first season after partnering up with Nightmare. He loses the title to X!Gaster after he's restored by Ink.
- Calling the Old Man Out: Him and X-event Frisk attempted to do just that with XGaster, but were swiftly ignored and brushed off as "ungrateful brats".
- Chaotic Evil: Definitely on the psychopathic side of things. Losing your SOUL will do that, especially if you're already a Well-Intentioned Extremist.
- Enemy Within: Is this to Cross up until 0.3.
- Freudian Excuse: He claims that he's only going so far because XGaster treated him and X-Event!Frisk so poorly in the past. Considering their father's attitude and actions, it really isn't a surprise he and his brother are mentally unwell.
- Hidden Depths: Although they butt heads pretty often, deep down he still cares about Cross. During his fight with Swap in 0.3 part 2, he briefly sees a vision of Cross tearfully telling him that this is not what their friends from X-Tale would have wanted. Right after that he uses his powers to heal Swap completely, admits to him that he actually misses being friends and even offers Swap to join him. When Swap shows no intention of backing down, he remarks that it was silly of him to think Swap would understand him, since at the end he's not really his Sans.
- Hypocrite: He seeks to punish XGaster and Ink for treating innocent people like they're their personal play-things and destroying lives for no reason other than that they can - by doing the exact same thing to every pacifist timeline he comes across.
- It's All About Me: He doesn't care that he's hurting innocent people. Every time he's cornered, he immediately starts squalling about how he is in the right, because of what XGaster did to him and his brother. When XGaster is eventually revived, all he does is scream about how he was supposed to win and how unfair this situation is to him.
- Really 700 Years Old: The flashback in 0.4 reveals that X-Event!Chara has grown up multiple times already, but is now stuck in his child form, due to his father's constant abuse of the OVERWRITE button.
- Red Oni, Blue Oni: The Blue Oni to Cross's Red Oni.
- Revenge: His main motivation for wanting to destroy the Alternate Universes. He wants revenge on XGaster for everything he did to him and his brother Frisk and on Ink for indirectly causing it all to happen in the first place. Destroying all of the timelines they admired so much seems like a good start to him.
- Kick the Dog: When they were still fused together he tended to verbally abuse Cross whenever he could, calling him nothing but a tool, mocking him for destroying the world he'd been trying to save and even attempting to take over his body without permission when he was already tired out and injured from his fight with Fell.
- Laser-Guided Karma: Throughout the first few episode he's done everything in his power to put Cross down and even called him nothing more than a tool in 0.2. By 0.4 the tables have effectively turned on him. Now he is the one constantly being abused and put down by a Reality Warper who can read his thoughts.
- Moral Myopia: Hates XGaster and Ink because they manipulate and use people for their own gain. He and X-Event!Frisk did the very same thing to Cross in the prequel comic and didn't even seem to feel sorry about it afterwards. Chara in particular started mocking him for destroying the world he'd been trying to save, though Frisk at least desperately tried to make amends to some degree before dying.
- Not So Different: He hates how XGaster and Ink lie to and manipulate people to get what they want, but the prequel comic shows he and X-Event!Frisk weren't exactly saints in that regard either.
- Psychopathic Manchild: He's Really 700 Years Old yet still feels the need to throw massive temper tantrums whenever something doesn't go his way, shows child-like glee at torturing innocent people and acts like his situation entitles him to the Overwrite-button and the multiverse.
- Sanity Slippage: Happened gradually in his backstory. Being forced to kill his own brother and becoming a pawn in XGaster's "game" was probably what drove him off the deep end.
- The Extremist Was Right: In 0.3 Part 2, he makes the assumption that Ink is secretly helping XGaster come back and is merely using the other Sanses to achieve that goal. 0.4 shows he was completely right.
- Too Dumb to Live: Insulting and attempting to order around an Eldritch Abomination, who is clearly already pissed at you, while you yourself are injured, pretty much powerless and stuck in a childs' body may not be what one would call a smart move.
- Used to Be a Sweet Kid: If the flashback in 0.3 Part 2 and what Nightmare says in 0.4 is anything to go by.
- Villainous Breakdown: Breaks down into tears when X!Gaster is restored at the end of 0.4, effectively nullifying his plans.
- Woobie, Destroyer of Worlds: His own father experimented on him and his brother over and over again, so he could create the perfect world. Trying to stop him is what ended up driving him insane, according to Nightmare.
- Antagonistic Offspring: Thanks to a combination of his father's perfectionist attitude and the X-Event experiment, he's very upset with him and actively revolts against him with his brother in the prequel comic.
- Back from the Dead: VI.VII shows him alive and well by XGaster's side.
- Big Bad: Of the prequel comic.
- Brainwashed and Crazy: Briefly becomes this in X-tale IV as a result of XGaster overwriting his code.
- Bitch in Sheep's Clothing: He is presented as a nice and caring person like most portrayals of Frisk, but after Cross refuses to kill him as a part of his plan, he drops the act and actively tries to eliminate him from then on.
- Break the Cutie: Originally, he was as nice as any other Frisk, but the X-Event experiment gradually took away any niceness he had until it made him into what he was by the time of the prequel comic.
- Creepy Child: What he is really like under his facade.
- Evil Former Friend: Him and Cross were best friends before he decided to manipulate his code. It didn't stop him and his brother from trying to kill Cross when he refused to play along with their Thanatos Gambit.
- He Knows Too Much: When Cross refuses to kill him, he tries to pull this but is stopped at the last second by XGaster.
- Impaled with Extreme Prejudice: A victim of this twice over. The first time, it's from Cross' entire arm which mortally wounds him. The second is from one of his giant knives which finishes the job.
- Karmic Death: In the end, he is murdered permanently by the very person he tried to manipulate into killing him before.
- Killed Off for Real: At the end of the prequel comic thanks to Cross until after the events of 0.4.
- Moral Event Horizon: Manipulating Cross' code in order to force him to kill him. When that doesn't work, he simply decides to kill him to prevent him from being an obstacle to his plans.
- Patricide: Him and X-event Chara nearly killed XGaster in the prequel comic.
- Tragic Mistake: Insisting on killing Cross himself out of anger even though he was already dying. This comes back to bite him hard, as it gives Cross an opening to impale him and absorb his soul.
- Tragic Villain: Just like his brother, the X-Event experiment caused him to become bitter and angry, willing to do whatever it takes to win the war for the universe.
- Well-Intentioned Extremist: What he appears to be in the prequel comics at first. He tries to get Cross to kill him in order to gain full control of the Overwrite button and overthrow XGaster. However he later reveals that this is not due to a desire to free everyone, but because he can't stand not being the one in control, like his main universe counterpart. Something Cross immediately realized and called him out on.
- Arch-Enemy: To Ink, who wants to protect the "anomalies" he hates so much.
- Big-Bad Ensemble: He's another major antagonist in the series, but has no connection to X!Gaster or X!Chara's plans, nor does he have any desire to work with them.
- Curb-Stomp Battle: Gives one to Swap, Fell, and Sans in 0.4, capturing all three of them effortlessly.
- Is on the receiving end of one right after that. An emotionless Ink is able to restrain and send him away in a matter of seconds.
- Even Evil Has Standards: Even he is disgusted by Ink's true nature.Error: You freaking psycho. I shouldn't have negotiated anything with you.
- Eye Scream: Those blue string he uses to grab things (and occasionally people)? He pulls them out of his eyesockets.
- Hates Being Touched: Very much so. It either causes him to have a Freak Out or to crash himself.
- Hybrid Power: He has normal Sans' attacks, but he executes his through blue puppet strings.
- Hypocrite: He makes a big deal about hating anomalies despite the fact that he is one.
- Marionette Master: His general theme. If he wraps another person's soul up in his blue strings, he is able to control their body and magic.
- The Corrupter: Hates most Alternate Universes, considering them to be "Anomalies", so therefore he corrupts and destroys them.
- Villain Has a Point: In "The Truce", he bashes Ink for endlessly helping to create more Alternate Universes, telling him that the Multiverse has a limit and could collapse if Ink keeps making more. He's right.
- Berserk Button: Trying to break a deal with him.
- Big Bad Duumvirate: He enters one with X!Chara, though it becomes a painfully one-sided partnership in Nightmare's favor by 0.4.
- Eldritch Abomination: It's not exactly clear what he's supposed to be. His body seems to constantly melt away and he's shown to produce tentacles from his back multiple times.
- Eviler Than Thou: Constantly reminds Cross that he is far more powerful than he is. X-Event!Chara gets this treatment as well in 0.4.
- Good Hurts Evil: Played straight.
- Kryptonite Factor: Happiness, and of course, his own brother, Dream.
- Motive Decay: His origin story gives shades of this.
- The Empath: Like his brother, Nightmare can sense emotions. His interest lies in the negative ones.
- The Man Behind the Man: To both X!Chara and Cross. His partnership with X!Chara drives most of the plot.
- Tragic Villain: In his origin story, he originally wanted people to love him, but got so desperate in his attempts to be a good guy that he corrupted himself. Now he wants everyone to feel his pain and thus fully supports genocide runs in any Undertale AU.
- Brainwashed and Crazy: Essentially what the Chara of his timeline did to him.
- Chaotic Evil: All he seems to care about is killing and hurting others.
- The Dragon: To Nightmare from 0.4 onward.
- Eviler Than Thou: He shows up X-Event!Chara very quickly, and is a closer accomplice to Nightmare than they are.
- Eye Scream: His eyes constantly drip with a black liquid that is said to be pure hatred.
- Knife Nut: His weapon of choice is a knife that bears an uncanny resemblance to the Real Knife.
- Non-Standard Character Design: His soul is unlike anything else seen so far. It's a red monster soul that is shaped like a target, and unlike other souls, is always seen on the outside of his body.
- Slasher Smile: His default expression is a menacing grin.
- Tragic Villain: Per his backstory, he was essentially forced by the Chara of his Universe to kill everyone. After he had done the deed, he was left unable to feel any emotion and was left a warped, broken shell of his former self.
Once the benevolent creator of X-Tale, XGaster longed to create the perfect world, but fell into despair when he was unable to do so. After meeting Ink and seeing the Doodle Sphere, he became inspired to try something new, the X-Event.
- Abusive Parents: At first, he was a genuinely loving father... then, after becoming obsessed with perfection, he experimented on his own kids to achieve his goals.
- Betrayal by Offspring: Considering what he'd already done to them by that point, it was more than Justified.
- Big Bad: Upon being freed, he effortlessly outclassed the Big-Bad Ensemble, setting himself up as the true main antagonist.
- Body Horror: Most of his body became deformed and melted due to the shred of Determination in his "soul" being all that kept him alive after the attempt on his life. He also has no legs courtesy of X-Event!Frisk cutting them off. Not that he needed them anyway.
- His "restored" appearance in 0.4 meets both his former appearances in the middle, looking much better than before but still a far cry from what he used to look like.
- Crazy-Prepared: Knowing that one day his sons would eventually rebel against him and try to take the other half of his soul, he entrusted it to Ink far before then in order to keep it from them.
- Driven to Suicide: In his backstory, he planned to do this after he failed to create something wonderful which would have destroyed X-Tale along with him. Ink is able to put a stop to this by showing him the Multiverse, reinvigorating his passion.
- Four Eyes, Zero Soul: Was this in his original form.
- Eldritch Abomination: Became this after his own sons tried to kill him.
- Eviler Than Thou: In 0.3 part 2, he provides some aid against X-Event!Chara, canceling out their use of OVERWRITE with his own half. It remains to be seen whether he genuinely wishes to protect the multiverse, simply didn't want the show to stop, was acting out of self-preservation, or some combination of the above.
- Greater-Scope Villain: Outscopes Nightmare of all people, in terms of just what he's doing.
- Hate Sink: Regardless of who he used to be, he is by far the most vile character in the entire show. He killed his sons' friends and described their anguish as "Exciting", brainwashed Frisk into doing a Genocide route, mentally scarring him in the process, and later has him try to kill Chara, mocking the latter while doing so and calling them "Ungrateful Brats" when they fight back. He is a sociopathic narcissist and responsible for nearly everything bad that has happened in the main story.
- I Did What I Had to Do: His general excuse for the horrible things he did in the X-Tale timelines.
- Lack of Empathy: He seems utterly indifferent to the suffering he's caused, both directly and indirectly.
- Man Behind the Man: Has been using Ink of all people to manipulate the cast, and get his full soul back.
- Motive Decay: As the "Creator" of X-Tale, he originally wanted the best for his two sons, X-Event!Chara and X-Event!Frisk. However, he became discouraged when he couldn't create the perfect world. After Ink shows him the Multiverse, he seems to be inspired again, but becomes so caught up in the X-Event experiment that his goal changes to wanting to see what interesting experiences his "game" will bring, no matter the cost.
- Never My Fault: Even before his sons rebelled against him, he utterly refused to take any responsibility for his less than moral actions, instead convincing himself that his sons were the ones in the wrong for attempting to call him out on it.
- Purple Is Powerful: His soul is this color, and if 0.4 is any indication, he is no push-over.
- Spikes of Villainy: Has a couple of spikes protruding from his shoulders.
- The Perfectionist: The main reason why he kept constantly OVERWRITING X-Tale. He wanted to create the perfect timeline, but was never truly satisfied with what came out of it, and so he kept on changing everything until he came up with the X-Event.
- Psychopathic Manchild: No matter what way he slices it, behind that sophistication, X!Gaster is a petulant child at heart. He treats the Multiverse as his own toy box, tampers with the lives of others, and can't even entertain the idea of being wrong.
- Walking Spoiler: Very much so for his role in the prequel comic and his status as The Man Behind the Man. His revival in 0.4 only makes him that much more of a spoiler.
- Beware the Silly Ones: He is far wackier than the original Sans, but he can be just as scary if not more so. Just ask Cross.
- Eldritch Abomination: He looks normal right now, but this is what he looks like with a host. His true form is much more terrifying.note
- Empty Shell: His base personality, lacking in emotions and being incapable of love. He hides it well under his "go with the flow" personality.
- Gag Censor: One of his abilities, which kicks in whenever someone tries to swear. It causes the word to become a Sound-Effect Bleep while also changing the word to one of his "Fresh words". Underfell!Sans learns this the hard way.
- The Thing That Would Not Leave: Not even Error can erase him.
- The Virus: To survive, he must continually jump from host to host so that nobody becomes suspicious of him.
- Neutral Good: They have no interest in taking an active part in the battle, but they will do what they can to make sure the survivors of the erased universes stay safe in the omega timeline.
- Not So Stoic: They don't show a lot of emotion when they first encounter Sans in Xtra Scene 1, but in 0.4, seeing the death of Underswap!Papyrus and being unable to help him drives them to tears.
- The Omnipresent: One of their powers thanks to their fall into the CORE. They use this in order to spy on X-Tale!Alphys while being in X-Tale with Dream.
- Badass Bookworm: Not the least bit impressed by Underfell!Asgore's threats.
- My Master, Right or Wrong: Despite clearly being uncomfortable with XGaster's actions in the X-Tale timelines, she never does anything to interfere with or even dissuade him from his plans. 0.4 implies there's some kind of Mind Manipulation at play.
- Not So Stoic: She seems to be completely emotionless at first, but after Underfell!Asgore attacks her, she seems to be pretty annoyed. This could very well also be XGaster speaking through her.
- Number Two: She is XGaster's loyal right-hand-woman.