[
  {
    "level": 1,
    "spawnInterval": 2000,
    "enemyTypes": ["grunt"],
    "enemyMultiplier": 1.0
  },
  {
    "level": 2,
    "spawnInterval": 1800,
    "enemyTypes": ["grunt", "brute"],
    "enemyMultiplier": 1.2
  }
]