Six "evil" skeletons that all work for Nightmare to cause negativity, chaos and destruction. Their enemy is the Star Sanses. 
Nightmare is the manipulative, rude boss.
Killer was the second to join the Bad Sanses and is obedient to Nightmare.
Dust is a quite, insane and traumatized one.
Error is the glitchy, narcissistic, tsundere.
Horror is the hungry, psychopathic one.
Cross is the newest and kindest of them all, though traumatized he just wants to restore his past.