The negative-energy-consuming leader who orchestrates multiverse corruption. Nightmare Sans (Leader)Physical Appearance: Covered in a black, sticky, negative-gop substance, with four to six shifting dark tentacles sprouting from his back. He has a single glowing blue/cyan or light-purple/green eye depending on the form, and a skeletal frame shaped by pure negativity. Personality: Cold, ruthless, arrogant, and sadistic. He feeds on fear and emotional torment, though he bizarrely maintains a toxic, pseudo-familial bond with his own team members to fill his internal void.

Error Sans: A glitchy destroyer obsessed with erasing anomalous or "error" AUs. Error Sans Physical Appearance: A glitchy, dark-boned skeleton covered in floating red and blue error-message text ("101010"). He wears a black jacket with a blue hood, black pants, and blue/yellow-tinted bones with glowing yellow-and-blue eye sockets that leak blue strings. Personality: Highly intelligent, extremely sarcastic, erratic, and deeply hates anomalies or "glitches"—yet secretly likes knitting and watching television in the anti-void.

Dust Sans: A murderer driven insane after repeatedly killing everyone in his timeline to gain LV. Dust / Murder Sans (Dusttale)Physical Appearance: Looks like classic Sans in a blue hoodie and black shorts, but his clothes and skull are caked in visible grey monster dust from everyone he killed, and his magic eye glows a volatile red and blue. Personality: Mentally unstable and haunted by the auditory hallucination/phantom of his brother Papyrus. He is quiet and distant around strangers, but deeply sadistic and tactical when hunting.

Killer Sans: A corrupted soul who gave in to his timeline's genocidal path and aligned with Nightmare. Killer Sans (Killertale)Physical Appearance: Resembles classic Sans, but with heavy black, inky "Determination" liquid dripping constantly down from his empty eye sockets. His visible soul often hovers outside his chest as a warped hybrid soul. Personality: Numb, unpredictable, and entirely lacking baseline empathy due to maxing out his LV (Level of Violence). He hides his inner psychological breaks behind a mask of sarcastic humor and manic grins.

Horror Sans: A brutalized, starving survivor from Horrortale bound to Nightmare's group. Horror Sans (Horrestart)Physical Appearance: A massive, thick-boned skeleton with a large, distinct crack in the top-left side of his skull. He often wears a blood-stained or dirtied hoodie and carries a giant meat cleaver or axe. Personality: Brutal and terrifyingly unhinged due to starvation in his home timeline, but ironically can act surprisingly calm, sweet, or detached when not actively violent.