Genocidal Gaster is the Gaster of a noncanon timeline in Glitchtale. In this timeline, Gaster resorts to killing humans and monsters in order to gain more LV, to be powerful enough to defeat Betty. This timeline is prior to Undyne's battle against Betty from "LOVE".



He was formerly a gentle, caring and kindhearted doctor, before Betty had killed both Sans and Papyrus. After that, he had became broken, lost, lonely, and eventually maniacal, deliberate, unstoppable and insane. He will kill anyone in his path from where he started to Betty, which had gained him LV to 49. Undyne and his friend, Pen, had fought him to try to stop him, succeeded and locked him up in prison. However, he escaped and killed the guards, despite them begging for mercy, showing a merciless shell of who he was. From killing the guards, his LV reached 50, and he set off to kill Betty once and for all. Unlike Killer, he still has emotions, and will begin to cry if he thinks about Sans and Papyrus, or is shown what he's done.


He has white bones and no hair. He is short. His face is cracked, and he has holes in his hands. His pupils and SOUL are dark yellow, for Vengeance.

He wears a grey sweater, black pants and black sport shoes. He also, from his personal fashion preferences, wears a white lab coat. He has dust and red stains on his clothes and hands from his genocide. He also wears Papyrus's red scarf, which he had taken before his genocide began.


He had sent Undyne and Papyrus to find clues about Betty, and had become enraged when all that returned was Undyne and Papyrus's scarf. Furious, he snatched the scarf from her and almost killed her, only to be stopped by Pen. Furious, he attacked the latter and swore his genocide, but was knocked out by Undyne. He was then bound, so he could do no harm. However, deep in the night, he got himself untied and snuck off. Undyne had seen him untied, and attacked, but was killed, making her his first kill. Since that, he had killed humans and monsters to gain enough LV to defeat Betty.

Weapons and Abilities

His regular attack is significantly more powerful. His DUALITY attack has been altered into "Necrophobia", which does not have the same effects as Betty's "Rhabdophobia", but has caused most of Gaster's kills. With "Necrophobia", he learns what is the one way the one he's fighting does not wish to die, and makes it a reality.


Unlike most genocidal characters on this Wiki, Geno Gaster still has emotions, making it incredibly hard to kill one close to him. This is first displayed when he has to fight Pen. He and her are close friends, thus he could not bring himself to harm her.



He cared deeply about Sans, and was devastated when he was killed. He initially wasn't as hurt, as Papyrus was still alive.


He cared deeply about Papyrus, and was enraged when, after Undyne and Papyrus's mission, only Undyne returned. At this point, his sanity had slipped away.


He has grown an intense hatred to her for "allowing" Betty to kill Papyrus. When she returned without Papyrus, he was enraged to the point of almost killing her, only to be stopped by Pen.


She is the only person he'll listen to. Because of him still having his emotions, he can't hurt her.


She is his nemesis. He is gaining EXP and LV to kill her.


  • Assuming classic Gaster's LV is 1, Geno Gaster's HP is incredibly high from multiplying his LV 1 HP with his current LV.