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

{
  "items": [
    {
      "default": {
        "item": "magma_cream",
        "count": 0
      },
      "conditions": [
        {
          "condition": "net.glowstone.util.loot.LootingUtil.isNot($.getSize(), 0)",
          "count": [
            {
              "chance": 0.25,
              "value": 1
            }
          ]
        }
      ]
    }
  ],
  "experience": {
    "count": 1,
    "conditions": [
      {
        "condition": "net.glowstone.util.loot.LootingUtil.isNot($.getSize(), 0)",
        "count": 2
      },
      {
        "condition": "net.glowstone.util.loot.LootingUtil.isOver($.getSize(), 2)",
        "count": 4
      }
    ]
  }
}