SD Dream

Has all the abilities of the regular Sans, but they are more dangerous and sick - the bones and teeth of the Gaster Blasters are sharpened;
Instead of blood when wounded, he bleeds the same black substance (hatred), but does not notice it.
Similar to his eyes, the sockets of his Gaster Blasters also ooze blackness evenly.

Nightmare is strong enough to be able to, albeit temporarily, force his brother Dream to retreat from a fight. His aura can affect the entire universe he is in and many others that are close enough. He does not need to move much to spread negativity, and he only does so to find people to torment. He can turn into a puddle and move around without being noticed. He is able to teleport through darkness. Nightmare can only visit AUs with negative emotions, such as Negatale. He uses bad emotions to manipulate people. He can change his shape, but usually maintains Sans' form because it suits him. He is also able to split himself in half to make multiple selves do different things. As shown in one of the animated clips from Joku, he can also absorb his slime into the ground, turning a large area into darkness. He uses his tentacles to fight, and to intimidate his enemies. The black slime that surrounds him is an extremely powerful shield, making him invulnerable to most things; if he were to be pierced by something, his body would absorb it and no damage would occur. This applies not only to physical ones, but also to magical ones.
Weaknesses
Positive is his main weakness that only Dream can exploit. This is the only way to defeat Nightmare.
Light is one of his weaknesses. If you illuminate a dark area, he can get injured.
He also completely fails to fit into positive AUs like Haventale or A Tale o Doggy. A similar thing happens to Dream in Horrortale.
Since he only has one eye to see, he has a blind spot.

Capabilities :

1. Magic bones with a sharp edge.

2. Teleportation to any place within 3 kilometers

3. With great difficulty he can use blue magic bones with a sharp edge.

Weapons: The arsenal of abilities is not large, so it has to be replenished with others:

1. Kitchen cleaver for chopping bones. Sometimes he carries it with him, but mostly he keeps it at the watch station.

2. Kitchen knives. Rarely uses them, and even then throws them away.

3. An old lumberjack's axe. He walks with it near the entrance to the snow-city, waiting for people. He doesn't take it for other occasions.

4. Several large, powerful bear traps.

Very ambiguous, maybe for a long time he is relatively calm, but at the same second he starts to panic or freak out. Due to the growing psychosis, his mood changes very often and abruptly

There are similarities with the original Sans. Time and the terrible world played a cruel joke on him. His jacket has become very worn out and darkened from a lot of time, torn in some places, which is noticeable. The fur on his hood is pretty worn out. The old white T-shirt is also torn, but the most noticeable thing on it is the large blood stains that have long dried on it. Black shorts with white stripes, like the T-shirt, are stained with blood. And cute pink slippers have turned into shapeless pink fur. There is a hole punched in the skull of This Sans, it is impossible not to notice. His left eye constantly burns red-bloody.

The killer looks like the original, but his jacket is dark blue with fur in the hood, a black turtleneck, in front of which his variable soul is always visible in red and white in the form of a target, and white shorts with black stripes. Instead of slippers, he wears gray-blue sneakers. His face changes depending on the state of his soul.

Killer has a clouded mind, thirsting to kill or bring pain to others, because it gives him pleasure. His soul is defective - it is something like a target from the side of the heart (if he has one at all). This is the result of the perfect balance of the monster's soul and the human soul (the inverted and normal hearts compensated each other). He has 4 states: the first - the soul looks like the monster's soul, but red and with a border, Calor can switch it to this mode; the second - the soul slowly rotates in the form of a target; the third - the soul becomes a solid cloudy spot, rotating at great speed (at this moment it no longer pulsates, as if the heart 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 the hatred from his eyes becomes almost solid. Interestingly, although Killer's soul was merged with Chara's, Killer has no Chara's mind, only memories of her.
Most of the time Killer!Sans is in the "second" state. During it, Killer is unpredictable, plays on the emotions of his victims, and is also very cruel: calmly kills others, without feeling guilty. A black liquid begins to flow from his eyes, which is a huge amount of determination (or just hatred), and the pupils disappear.
Occasionally, Killer enters the first state: during this state, Killer can feel some kind of emotion, is calm and predictable, and his "tears" disappear. In the third state, Killer is furious and attacks everyone.
Sometimes Killer starts to feel guilty, but he consoles himself by saying that others will forget everything. Sometimes Killer also remembers Papyrus' death, for which he blames himself. Also, part of his soul does not want all this and wants his friends and family back.

His current appearance is quite sinister. You can only see the outline of shorts, a hoodie and slippers. He is completely black, with 4 tentacles that he can remove at will, coming out of his back. His left eye constantly glows blue. This is due to the fact that his body is unstable and therefore constantly "melts". Nightmare is quite attracted to negative emotions and he will do everything to get as many of them as possible, that is, killing victims does not make sense to him, since without them there will be no negative emotions he needs. However, he kills those who break contracts with him, or makes him remember what he was like in the past, before corruption, or when he is pissed off (though in this case, he will still try to make his victim suffer and experience the deepest negative emotions, such as doom, despair or other similar emotions).
Nightmare never lies, he only hides the truth. He takes deals to heart, which is why he kills those who break them without question.

Dream wears a huge kurta, a shirt, blue pants and boots. And above his head, a halo constantly flies.

Dream has huge wings that he can spread at any time and with their help he flies. His eyes are of different colors: the right eye is yellow with a red pupil and the left is red with a yellow pupil, which becomes similar to the sun when he is at the peak of his powers. He is also much taller than the original Dream or Nightmare.

Before Swap Dream ate 999 golden apples, his personality was exactly the same as the original Dream.

Swap Dream is incredibly arrogant, he considers those who are weaker than him to be pathetic, and if he finds someone who is stronger or on the same level as him, he will immediately rush into battle, laughing madly.

After eating 999, he went completely crazy. He is very rude, and will easily throw insults at anyone he doesn't like (almost everyone) as well as just showing someone the middle finger.

Dream cannot feel true love, but because of positive emotions, he constantly tries to achieve it in every possible way.

Dream is incredibly strong, he can use positive emotions to create any torture instruments or weapons he needs. Starting with ordinary daggers or shields, ended with ropes and chains. Also the ability to move through universes thanks to positive emotions.

Dream has 2 main weapons, these are: Blue daggers resembling lightning, the handles of which are connected by a long chain, they are incredibly sharp and dangerous to others. And also, a huge bow.