Killer Sans was made by Tumblr user Rahafwabas.
In a genocide route, Chara convinces Sans to commit genocide with them multiple times by manipulating him through new experiences. After several genocides, Sans' emotions disappeared and his eyes began to expel liquid hatred. He also has the power to reset. There seem to be 3 alternate timelines of Killer!Sans where:
#1: He killed Chara and continued on his genocide.
#2: He joined Chara and made a partnered genocide.
#3: He joined Chara but later decided to leave them and continue his genocide.
Note: #2 and #3 are the most common versions.
Sans looks very similar to Classic Sans, but his eyesockets are spilling what's left of his eyes as they could not withstand the determination and only his right eye glows white because of the magic that still resides in that eye. He still is a skeleton with a blue sweatshirt. His soul is also different and it actually shows all the time, unlike Frisk's, whose soul only shows in battle, but his soul also looks different because it looks kind of like a red target.
Sans went insane after the genocide runs and feels no real emotions.
Real Knife: Causes 99 damage.
Sharp Bones: Usually has high attack but deadly when attacked at the sharp point.
Way More HP: Because of him having determination like Chara, he has gained way more health points than most other Sans, though it's unknown how much exactly.
Reset: He has the power to reset the timeline, but if he does this his stats will be reset, making him LV 1 again but still with his twisted mind, though he can save which makes up for his reset.
Note: Killer!Sans has no Gaster Blasters... but he has one giant goop-spilling Gaster Blaster though It's full power is unknown, he uses it either when he's bored of his opponent or wants to end the fight very quickly
Killer!Sans loves to mess around with him. He is one of the only people who Nightmare talks with normally. He's the leader of the Nightmare Team in which Killer!Sans is included and is a valuable member. Nightmare keeps check of Killer that he remains in his dark state by reverting his soul back to its emotionless state from time to time, though Nightmare has a big rival when it comes to the soul of Killer, which is Color!Sans.
Genocide partner or purely hated rival. It depends on the user.
Another version of Sans who used the six souls in the genocide route. He is a dear friend to Killer even though he gets annoyed sometimes by him. He tries to revert Killer back to his normal good self, but Nightmare keeps check of Killer to stay emotionless.
They met in another world where he tried to immediately kill Underswap and since then they've been on not so great terms.
- He has an LV of 20+
- He won in a fight between Ink!Sans and Cross!Sans.
- He is a pretty loyal member of Nightmare!Sans' team.
- He destroyed his own Gaster Blasters because he wants to have a challenge.
- He is actually a jerk.
- He likes to make fun of Nightmare!Sans and usually gets punished for doing so...
Note: His soul is unstable since it can revert back to normal with some help, and as a result this rival battle between Nightmare and Color begins. Nightmare seems to like Killer in his state and reverts Killer back to the killer he is whenever he feels emotions again, and Color tries to revert Killer back to normal but Nightmare always gets in the way.