How to store a prefab in a variable

When the drop() method is called, is the bobberPrefab variable null or otherwise invalid?

After the Instantiate() method is called, is the bobber variable null? Maybe Instantiate() failed for some reasons.

I can't see your code where you're destroying the bobber, but I'll assume that it's in an other method.

Your bobber variable is a reference to the GameObject that Unity gave you after calling Instantiate(). It's also a local variable, meaning that at the end of the drop() method, all local variables will be deleted. Since bobber is a GameObject created through Instantiate, Unity will keep track of it and it won't be destroyed at the end of drop(), but your way of talking to it will lost.

You should store your newly created object in a variable with a higher scope, in a class member variable.

 class MyClass : MonoBehavior
 {
    [SerializeField] private GameObject bobberPrefeb;
    private GameObject bobber;

    public void Drop()
    {
       bobber = Instantiate(........);
    }
 
    public void KillBobber()
    {
       Destroy(bobber);
    }
 }

I don't know if this code is supposed to manage only one or many bobbers.

• If it's only one, either make sure Drop() cannot be called more then once if (iWantToCreateABobber && bobber == null) { Drop(); }, or the method does nothing if the bobber already exists if (bobber != null) { return; }. Or destroy the previous object before creating a new one.

• If it's many, then replace the bobber member variable by an array, a list or some other type of collection and adjust the code to store it, then find a way of destroying the correct one.