Limit looping background in 2d?

your post is kind of misleading, your use of the term "background". But I can help you with the looping problem

To set this up

1. Create your zombie GameObject and a new folder in the assets folder called "Resources" this will be used for Resources.Load and Instantiate.
2. Next drag your zombie GameObject into the Resources folder to create what is known as a prefab.
3. Click on it so the components of the prefab show up in the inspector, on the Transform (very first) component click on the gear>Reset Position so the zombie spawns right on the spawner rather than however far away.
4. Add the following code to a CSharp script:

SpawnerScript.cs

 int loopingLeft;
 
 int loopingTimeout;
 
 void Awake(){
     //assign in Awake just in case
     loopingLeft = 25;
     loopingTimeout = 0;
 }
 
 void Update(){
     if(loopingTimeout == 0){
         if(loopingLeft != 0){
             //clone the zombie
             //To clone the zombie drag the original "GameObject" into a new 
             folder called "Resources" so you can access and duplicate the 
             zombie using Resources.Load the gameobject you duplicated is called a prefab. The gameObject.transform is so the zombie spawns in the spawner gameobject.
             Instantiate(Resources.Load("zombie") as GameObject, gameObject.transform);
             loopingLeft--;
             loopingTimeout = 100;
         }
     }else{
         loopingTimeout--;
     }
 }