ItemsAdder

https://www.spigotmc.org/resources/73355/

For items:

material: ItemsAdder:namespace:id

For blocks:

block: ItemsAdder:namespace:id

For mobs:

mob: ItemsAdder:namespace:id
properties:
  frustumCulling: false  # if this entity needs to be frozen if not visible by the player.
  noBase: false  # if this custom entity doesn't have a Bukkit real entity as base
  noHitbox: false  # if this custom entity bones have the armorstands hitboxes or not