src/main/resources/builtin/loot/entities/wither_skeleton.json

{
  "items": [
    {
      "default": {
        "item": "bone",
        "count": {
          "max": 2
        }
      }
    },
    {
      "default": {
        "item": "coal",
        "count": {
          "max": 1
        }
      }
    },
    {
      "default": {
        "item": "skull",
        "count": [
          {
            "chance": "0.025",
            "value": 1
          }
        ],
        "data": 1
      }
    }
  ],
  "experience": {
    "count": 5
  }
}