spawn.json

[
  {
    "dimension": -1,
    "mob": "minecraft:wither_skeleton",
    "result": "allow"
  },
  {
    "dimension": -1,
    "mob": "minecraft:wither_skeleton",
    "onjoin": true,
    "mincount": {
      "amount": 50,
      "perchunk": true
    },
    "result": "deny"
  }
]