Geno!Sans

Geno is very manipulative and will continue to manipulate Sans to gain his trust after erasing his mind over and over until he finally gets his way.

He blames both Chara and Frisk for the genocide runs and calls them "his murderer". He is desperate to convince the current Sans to follow his plan, even if he has to use force.

He is also very sensitive about Papyrus and will not let anyone touch his scarf. When Sans brings Papyrus with him on his visit to the Save screen, Geno becomes furious.

While he can be quite violent, he still has a sense of humour, and his first reaction to seeing Sans is to make puns.

Geno's personality changes seem to be due to him not having a full soul, making him violent.

Like the original Sans, Geno has an unzipped hoodie jacket with a white shirt underneath, along with short pants and fluffy slippers. However, he has some differences to classic Sans. Geno's jacket and slipper are completely white, he has a huge bloody gash that he got after being hit in the Genocide run, along with blood coming from his mouth, and some having dropped onto his slippers. He wears his timeline's Papyrus' scarf, which he is very protective of, treating it as if it really was Papyrus. Also, because he wasn't supposed to be able to enter the Save screen, he is seen with white glitchy particles around him, one of which is covering his right eye socket, which he can control. Due to having injected determination into himself, Geno Sans placed those particles there on purpose to hide the part of his skull that's melting off due to injecting himself with Determination. He does this to ensure that Sans and Frisk would not be frightened.

Geno has all of Undertale Sans' attacks and abilities, including Bones, Blasters, and teleporting. He can bring others into the save screen, but seemingly only when they are making contact with Sans Due to his location in the save screen, he is unaffected by resets and can't die. It's unclear if this is due to an external factor or a new ability, but Geno can control glitches around his body, primarily to hide his melted head. With his large amount of Determination, he can remember resets and erase the timeline if he is inside it.

He cries a red liquid presumed to be blood. The yellow part of his eye is now red due to his determination. His eye can go red when angry. He is unable to die while in the Save screen due to it having halted time.

Aftertale Geno is a Sans who was able to leave a Genocide timeline, escaping to the Save screen. Calling himself "Geno", due to him no longer feeling he deserves to be called Sans. He is stuck at the save screen with Frisk due to his mortal wound. Geno wants to completely destroy the universe, seeing it as the only way to end Papyrus's repeated deaths, but as he cannot leave the Save screen due to his minimal hp, he tries to get the other sans to do it. If they continually disagree, then he will erase his mind and will start over again. During the events of Aftertale, he stopped doing this so that the current Sans will remember all the resets and Genocide routes in the previous timelines in hopes to get him on his side.

Geno "survived" the Genocide timeline by injecting himself with determination, and before dusting away due to Frisk's attack, he escapes outside the timeline to the Save Screen, where he resides.

His mission is to destroy his timeline by stopping Chara, and erase the universe. However, he cannot do it himself because, if he leaves, he dies and Chara will still be in control. So, he tries to convince Sans to bring Chara to the save screen to get them out of the way. He will then attack them until they fall into a coma and then teleport out of the save screen to end the timeline because he will then be the one with the most determination, and therefore have control over the timeline.