Killer!Sans^^

Occupation: Serving Nightmare
Date of birth: January 19, 2016

Relationship :

Nightmare is the boss
Error is an ally
Horror! Sans is an ally.
Murder!Sans is an ally.
Swapfell!Sans is an ally.
Color!Sans — friend/bro
Epic!Sans is a friend
Ink!Sans is the enemy
Cross!Sans is an enemy
Additional facts:
• The best person to spend time with, besides Color and cats, is Swap!Sans.
• The killer loves cats.
• A killer can act like a real professional assassin - track down his target, analyze information about him, gain his trust and kill unexpectedly.

Killer Powers:
The killer tells Color about his first, second, and third states, asking him to kill him in the third, as he has already resigned himself to death. Color, however, doesn't want this and tries to find a way to restore his soul.
Meanwhile, Chara reminds Killer of another fourth condition, which Killer didn't mention. So, Killer kept quiet about what's wrong with best friends. After all, Sans doesn't want "another bad ending," as Chara puts it.
Capabilities :
• Has all the abilities of the regular Sans, but they are more dangerous and painful - the bones and teeth of the Gaster Blasters are sharpened;
• Instead of blood when wounded, he bleeds the same black substance, but does not notice it.
• Similar to his eyes, the sockets of his Gaster Blasters also ooze blackness evenly.

Appearance :
The character looks like a normal Sans. His jacket is a more grayish hue with cream-colored fur on the hood. His shorts are white with black stripes. A red circle is located on his chest—this represents Sans and Chara's soul. He also has mascara leaking from his eye sockets, which he can control during this process. At certain points, depending on the situation, barely noticeable pupils become visible in his eye sockets. This most often occurs when Killer experiences strong emotions, such as anger.

Personality:
Killer has a clouded mind, craving to kill or hurt others because it gives him pleasure. His soul is defective—it is a kind of target on the side of his heart (if he even has one). This is the result of a perfect balance of the monster soul and the human soul (the inverted and normal hearts cancel each other out). He has four states: first, the soul looks like a monster soul, but is red and has a border. Color can switch it to this mode; second, the soul slowly rotates in the shape of a target; third, the soul becomes a solid blur, spinning at an incredible speed (at this point, it no longer pulses, as if the heart has stopped); Nightmare is able to switch the soul to this mode. The fourth state is a kind of "berserker mode," in which Killer is completely uncontrollable, and hatred covers his entire face, while his bones turn red, including his attacks. In the third state, Killer is completely obedient and ceases to doubt anything, attacking everyone, regardless of whether they are friend or foe. His emotions are unstable, and all he sees are his targets, without distinction as to individuality.
What happens to Killer in the fourth state is unknown, but it is many times more dangerous than the third state.

Background:
He used to be a normal Sans, but later joined the genocide due to a deal with Chara. He killed all the characters in his AU and took the name Killer. The only murder Killer truly regretted was Papyrus. After his brother's death, Killer had nothing left to regret, so subsequent murders didn't bother him. He always carries a knife, which he uses as his primary attack. Later, Killer realizes that Chara are useless to him. They try to convince Killer otherwise, but the skeleton kills them anyway. Killer then comes to Nightmare and explains that by killing Chara, he gained control of his universe and was able to cast off all his evil deeds. He then bids farewell to his brother, believing he no longer has the right to be with him after killing him. He then becomes Nightmare's right-hand man.