Mob.yml
 ----------------
ChaosRider:
  Type: Skeleton
  Health: 20
  Display: "&bChaosRider"
  Skills:
    - skill{s=goldsworddamage;sync=true} ~onDamaged

Skill.yml
----------------------
goldsworddamage:
  TriggerConditions:
    - entityType{type=PLAYER}
    - wearing{m=golden_sword;s=HAND;} false
  Skills:
    - CancelEvent