assigning a variable to a instantiated gameobject and destroying it on another script

If you mean you want to get a reference to the instantiated object, you only need to look at the API docs to see an example (Google "unity instantiate", first result)

 Missile clone = (Missile)Instantiate(missilePrefab, transform.position, transform.rotation);

Instantiate() returns the clone object.

If that's not what you mean... You can not "add variables" or destroy them runtime. You have to write classes that have the variables you need and then assign different values to those variables. E.g.

 public class MyClass : MonoBehaviour {
     public string myString;
 }

And then

 GameObject go = Instantiate(characters[charindex], animalpos, transform.rotation);
 MyScript script = go.AddComponent<MyScript>();
 script.myString = "some text";

or if your gameObjects are prefabs that already have scripts attached to them, use GetComponent<MyScript>(); instead of AddComponent.

This is all very very basic Unity programming that has been covered here before and is covered in the Unity scripting tutorials too. I recommend checking them out.