A gameobject that behaves differently whether it is a prefab or a runtime object.

SelfCreatingPrefab.cs

using UnityEngine;

public class SelfCreatingPrefab : MonoBehaviour
{
    private int fieldA;
    private int fieldB;

    public SelfCreatingPrefab Init(int arg1, int arg2)
    {
        if (!gameObject.scene.IsValid())
        {
            var runtime = Instantiate(this);
            return runtime.Init(arg1, arg2);
        }

        fieldA = arg1;
        fieldB = arg2;

        return this;
    }
}