GameEvent.cs

using UnityEngine;
using System.Collections.Generic;

[CreateAssetMenu(fileName = "GameEvent", menuName = "~/Assets/Scripts/GameEvent", order = 0)]
public class GameEvent : ScriptableObject
{
    private List<GameEventListener> listeners = new List<GameEventListener>();
    public void Raise()
    {
        for (var i = listeners.Count - 1; i >= 0; i--)
            listeners[i].OnEventRised();
    }

    public void Register(GameEventListener listener)
    {
        listeners.Add(listener);
    }

    public void Unregister(GameEventListener listener)
    {
        listeners.Remove(listener);
    }
}