|“||LET'S SEE WHAT YOU'RE CAPABLE OF BEFORE KILLING YOU, EXPERIMENT.||„|
|~ XGaster telling his experiment|
XGaster is a major character and eventually the True Main Antagonist of X-Tale and Underverse. Failing to create a perfect world, he suddenly gets an idea to create one once he's shown the multiverse by Ink!Sans. He uses each idea from each AU into his universe, but his constant experimentation meant his own creations started to rebel against him, leading to his creation of the X-Event and subsequently watched over each and every thing his experiment does, even if it's outside his own universe.
- See also: XGaster/Entries
XGaster is first greeted by Ink after his agreement to Error!Sans's truce. He and Ink became friends, with the latter showing him the multiverse for any ideas for his universe. He soon gets approval by Ink to start his own experiment regarding the Overwrite button.
He first starts his experiment by introducing monsters to X-Tale!Frisk and X-Tale!Chara, but after a while he began to make strange experimentation to his universe for perfection, ranging from killing everyone to make everyone miserable, making a universe similar to Underswap, and doing a genocide route, which the children hate. In the fifth timeline, they both go against XGaster, but he eventually gets control of X-Tale!Chara, who rebels against his brother. XGaster would soon merge the brothers together under one soul and half of his soul in an attempt to keep them from ruining his fun, and allowing his access to the reset function.
XGaster acts as the father of X-Tale!Sans and X-Tale!Papyrus, and acts ignorant towards them, even ignoring the taste of X-Tale!Papyrus's spaghetti. After X-Tale!Frisk forces X-Tale!Sans to kill him, XGaster intervenes, and eventually resets to have it go the way it should. Once the party begins, however, he is struck back after he finds his X-Event missing. Once X-Event!Frisk returns with X-Tale!Sans, he arrives to impale the two of them, threatening reset as well.
However, this didn't erase the memories of all of his characters, and they got him back for manipulating X-Tale to his likening. When XGaster refused to give the X-Event the location of his other half of the Overwrite button, he loses his legs to them, and once Cross comes up, he shoves him out of the hall towards a forest, where he meets X-Tale!Alphys and tells her to store his entries. He slowly fades away, evaporating the universe, waiting until the X-Event shows him something amazing for once.
XGaster makes a brief appearance in Part 4, where after Sans is knocked down from the volleyball Undyne slammed into him.
Sans soon talked with Cross over what he's seen that day, and would unleash at them if he found out he's in league with them. He also makes a brief appearance before the episode starts, hinting to the next episode.
XGaster makes multiple appearances throughout Underverse 0.3. He's seen among a crowd of monsters when Cross slashed Underswap!Toriel's right eye. He appears once again when X-Event!Chara is about to impale Ink, overwriting Underswap!Sans and Underswap!Papyrus, saying in wingdings "YOUR CREATIVITY IS A SHAME", and more wingdings text appears throughout the battle, saying "YOU DONT DESERVE THE GIFT OF CREATING" and "YOU ONLY HAVE THE GIFT TO KNOW THAT YOUR USELESS LIFE IS NOT GOING TO END WELL"; he appears again when Underswap!Sans tells him what has harmed X-Event!Chara won't heal him; he's also seen side-by-side with Ink when X-Event!Chara tells Underswap!Sans that he's mad at him and he makes multiple comments throughout the entire battle.
XGaster appears again in Error's dream; after Ink eliminates Asgoro and Sins, XGaster proceeds to inform Error that this game is getting more interesting, and that he needs to wake up.
XGaster's role has been much expanded upon, looking at what Error has caused and the damages the X-Event has concurred. He's very upset at what they've done to Underswap(for Pragmatic reasons of course), and especially irritated when the cast from Underfell stops his assistant from continuing her task.
After Ink frees his soul from his vial, XGaster proceeds to hand Ink a new paintbrush and trap Error in his own dimension after he refused to negotiate with them. Reuniting his other half of his soul from the X-Event, he lets X-Event!Chara die, before proceeding to kill off Underswap!Sans and Underfell!Sans and transporting Sans back to his own universe. Knowing what he's doing, which is to create a single universe, he gives X-Tale!Chara another chance, revives Cross, and simply leaves him alone after reminding him to come and join his puppets.
His appearance bears a X strap around his coat and shirt, and a belt with a X strap around his pants. During his time with the determination he gained from X-Tale!Frisk and X-Tale!Chara, his appearances in Underverse is a semi-melted version of his real self. Thanks to X-Event!Frisk, he has no legs, which doesn't matter as he can still float around to move.
XGaster is the sole creator of X-Tale, allowing him to use the Overwrite button at will. However, he loses some control over it after he sent half of his soul to the X-Event. This allows him to reset, but destroys any chance of using the Overwrite button. His reset button doesn't even restart the whole timeline again; it brings back everyone to their normal position, but fails to erase any memories that the characters had before.
XGaster is more of a mysterious character, showing his isolation to the main characters except in special times, such as when X-Tale!Sans attempts to murder X-Tale!Frisk on stage. He's also a very clever man; knowing that everyone would soon revolt against him, he took his own soul and handed it to Ink for safekeeping.
Despite this, he shows much more borderline sociopathic and abusive tendencies towards his children, seeing them more as "experiments" than anything else. He barely cares about anyone's else feelings, and only wants them to fall into his own hands, using them as a puppet to his advantage.
The Animated prequels display that he was once a genuinely kind being, simply wanting to make a perfect world for his children. However, as time went on he shed every redeeming quality he once had and he became more and more cruel as he grew more and more desperate for his "perfect world". He even displays several signs of outright sadism, finding the anguish his sons had after he killed Asriel and Asgore "exciting," and then after brainwashing Frisk into a killer, he mocked Chara, saying "Frisk wants to play with you".
He is also shown to be extremely obsessed with control and shows several traits of narcissism, ranting about his kids for fighting back, accusing them of being "ungrateful". He also calls the other universes that aren't his own "garbage". This all shows that beneath his stoic, calculating demeanor he is mentally a child, seeing his universe as a toy box.
| X-Tale: Cross | X-Event!Chara | X-Event!Frisk | XGaster | X-Tale!Papyrus | X-Tale!Undyne | X-Tale!Toriel | X-Tale!Asgore | X-Tale!Asriel | X-Tale!Mettaton | X-Tale!Alphys