BallVictoryTriggerer .cs

using UnityEngine;
using System.Collections;
using System.Collections.Generic;

public class BallVictoryTriggerer : MonoBehaviour {
    void OnEnable () {
    }

    void OnDisable () {
        GameManager.OnGameEndingTriggered -= Asdf;
    }

    void Update () {
        if (Input.GetKeyDown(KeyCode.Space)) {
            GameManager.OnGameEndingTriggered += Asdf;
            print("bola avisándole a game manager");
            GameManager.TriggerVictory();
        }
    }

    public void Asdf (GameMode mode) {
        print(mode  + "!!!!!!");
    }
}

GameManager.cs

using UnityEngine;
using System;
using System.Collections;
using System.Collections.Generic;

public class GameManager : MonoBehaviour {
    public static GameManager instance;
    public static event Action<GameMode> OnGameEndingTriggered;

    void Awake () {
        if (instance != null && instance != this) {
            Destroy(this);
            return;
        }
    }

    public static void TriggerVictory () {
        if (OnGameEndingTriggered != null) {
            print("game manager disparando el evento");
            OnGameEndingTriggered(GameMode.Victory);
        }
    }
}

UIManager.cs

using UnityEngine;
using System.Collections;
using System.Collections.Generic;

public class UIManager : MonoBehaviour {
    void OnEnable () {
        GameManager.OnGameEndingTriggered += Avisar;
    }

    void OnDisable () {
        GameManager.OnGameEndingTriggered -= Avisar;
    }

    public void Avisar (GameMode gameMode) {
        print(gameMode);
    }
}