My first mobs, but has item bugs!

Hi, this is my first time making mobs. I dont know why it is use stone as head, i give him skeleton head with player skin. And some of the skills wont work, like summon. PLZ HELP .If there any more bugs. thx



AncientKing:
Type: WITHER_SKELETON
Display: '&0&k| &5&9Ancient &5King &0&k|'
Health: 500
Damage: 20
Options:
MovementSpeed: 0.35
Modules:
ThreatTable: true
DamageModifiers:
- LIGHTNING 0
- FIRE 0
- MAGIC 0
- PROJECTILE 0.1
- ENTITY_ATTACK 0.25...

My first mobs, but has item bugs!