create a mob that looks like a Skeleton which has the following appearance: 'Killer!Sans appears as a short, skeletal humanoid resembling the classic Sans, but with a dark, menacing twist. His skull is cracked and bleeds faint red veins, his eye sockets glow with piercing red light—his right eye pulsating like a flickering, deadly ember. He wears a torn black jacket with crimson-stained sleeves, a shredded white T-shirt underneath, and dark pants streaked with blood. At his chest, a red heart-shaped core pulses ominously. Cracked bones occasionally shift beneath his tattered clothes, and ripped fabric hangs like fractured memories. When idle, he clenches a twisted blade—his “True Knife”—and his grin stretches unnaturally wide, suggesting something horrible waits just beneath the surface.' and the following behavior/capabilities: 'Killer!Sans wanders the world silently until he spots the player, at which point his demeanor turns instantly hostile. He’s relentless in combat, teleporting unpredictably across short distances to strike with his knife before vanishing again into the shadows. He uses bone-based attacks—shooting bone projectiles in arcs—and summons "Gaster Blasters" made of pulsing red energy from his core. Each strike with his knife drains the player's health over time, stealing vitality. He also uses a terrifying ability to rewind brief moments in battle: if he takes significant damage, time briefly rewinds, healing him and resetting his position.
If the player tries to flee beyond 20 blocks, he warps back with a bone-cracking teleport accompanied by a chilling whisper. Upon death, he explodes into a shower of cracked bone shards and drops his True Knife (a custom weapon) plus a redstone heart—used to craft powerful reset-themed items.'
