private void OnEnable()
    {
        _enemy          = GetComponent <Enemy>();
        _missionTracker = GameObject.FindWithTag("LevelMissionTracker").GetComponent <LevelMissionTracker>();

        _enemy.KilledByPlayer += OnKilledByPlayer;
    }
 private void Start()
 {
     _missionTracker = GameObject.FindGameObjectWithTag("LevelMissionTracker").GetComponent <LevelMissionTracker>();
 }