Добавил переключение режима после уничтожения последного врага

Assets/Scripts/EndWaveStateSwitch.cs

@@ -0,0 +1,23 @@
+using UnityEngine;
+using System.Collections;
+
+public class EndWaveStateSwitch : MonoBehaviour
+{
+    [SerializeField] private GameManager _gameManager;
+    [SerializeField] private SpawnDeathEnemyController _spawnDeathEnemyController;
+
+    private void OnEnable()
+    {
+        _spawnDeathEnemyController.OnLastEnemyDestroyed += OnLastEnemyDestroyed;
+    }
+
+    private void OnDisable()
+    {
+        _spawnDeathEnemyController.OnLastEnemyDestroyed -= OnLastEnemyDestroyed;
+    }
+
+    private void OnLastEnemyDestroyed()
+    {
+        _gameManager.CurrentState = GameManager.GameState.BuildingTurrets;
+    }
+}

Assets/Scripts/EndWaveStateSwitch.cs.meta

@@ -0,0 +1,2 @@
+fileFormatVersion: 2
+guid: 78768dd3999d2ea4a80ad7a46bbf27a6

Assets/Scripts/SpawnDeathEnemyController.cs

@@ -4,7 +4,6 @@ using UnityEngine.Events;
 
 public class SpawnDeathEnemyController : MonoBehaviour
 {
-    [SerializeField] private GameManager _gameManager;
     [SerializeField] private EnemySpawner _enemySpawner;
     [SerializeField] private Wallet _wallet;
     [SerializeField] private UnityEvent _onLastEnemyDestroyed;