Bad Sans meets Karen

Nightmare (leader)
Killer
Cross
Horror
Error

Nightmare is the leader of the gang, a former guardian of the dark side of the Tree of Feelings and Dream's brother.

Personality: Cruel, cold-blooded, manipulative, and arrogant. He revels in the suffering of others and feeds on pure negativity, which makes him stronger.

Appearance: Completely covered in a thick, liquid black substance (negative energy). Four powerful, mobile tentacles extend from his back. The only visible facial feature is a single, glowing turquoise eye, or left eye. On his head, he wears the remains of his old golden crown, now darkened.

Abilities: Practically invulnerable to physical attacks due to his liquid body. Tentacles can pierce any obstacle, strangle, and grab enemies. Can teleport through shadows and manipulate the negative emotions of others.

Killer is Nightmare's right-hand man, a crazed killer from a universe where he succumbed to Chara's influence and committed genocide.

Personality: A psychopath, sadist, and cynic who has completely lost the ability to feel pity, fear, or love. He enjoys toying with his victims and often cracks crazy jokes.

Appearance: He resembles the classic Sans, but thick black lines (hatred) constantly flow from his eye sockets. Instead of a normal heart, his chest contains a soul in the shape of a target, symbolizing his complete apathy and instability.

Abilities: A master of close-quarters combat using a real knife. His attacks are incredibly fast and deadly. He can use modified Gaster Blasters that fire bows of lasers.

Cross is the sole survivor of the erased X-Tale universe, whose body has long held the soul of X-Chara.

Personality: A silent, serious, tactical soldier. Unlike the rest of the gang, Cross has some morality—he joined Nightmare not for the sake of chaos, but in the hope of restoring his ruined homeworld. Because of this, he often clashes with the other "bad guys."

Appearance: He wears a monochrome black and white suit, reminiscent of the royal guard, with white belts crisscrossing across the chest. He wears a long, fluffy hood. His right pupil is white, his left is red.

Abilities: Fights with a huge glowing purple knife (HACK knife). Capable of overwriting the code of objects (OVERWRITE ability), teleporting, and summoning giant cross-shaped bone attacks.

Horror is the insane and eternally hungry Sans from the Horrortale universe, where after the neutral ending in the Dungeon, a severe famine set in.

Personality: Mentally unstable, wild, but straightforward in his own way. Most of the time, driven by primal instincts and the desire to find food. However, he has a twisted sense of humor and is loyal to the gang as long as Nightmare feeds him.

Appearance: He has a massive crack/hole in the left side of his skull (resulting from a blow from Asgore). He wears a dirty jacket stained with blood. His left pupil glows with a large, insanely bright red dot.

Abilities: Relies on brute force in combat. His primary weapon is a huge, bloody axe or butcher's cleaver. He makes extensive use of sharp bones that sprout from the ground to trap his victims.

Error is a glitchy world-destroyer that considers all alternate universes to be "coding errors" and trash to be destroyed.

Personality: A loner, hot-tempered, selfish, and extremely nervous. He suffers from haptophobia (an extreme fear of being touched by others). He doesn't formally submit to Nightmare, but rather acts as a temporary ally with his own personal goals (to destroy everything Ink has created).

Appearance: His body constantly "glitches," becoming covered in pixels and "ERROR" signs. His skull is black, his teeth are yellow, and his eye sockets are red inside with multicolored pupils. He wears a dark blue jacket with a yellow lining. Blue streaks, resembling tear stains, run from his eyes.

Abilities: Produces strong blue threads from his eye sockets, which he can use to bind enemies, capture, and instantly destroy their souls. He controls lasers from distorted Error Blasters and can travel through the Anti-Void.