20200205-rundelayed-extension.cs

public static class MonoBehaviourExt
{
    public static IEnumerator DelayedCoroutine(this MonoBehaviour mb, float delay, System.Action a)
    {
        yield return new WaitForSeconds(delay);
        a();
    }

    public static Coroutine RunDelayed(this MonoBehaviour mb, float delay, System.Action a)
    {
        return mb.StartCoroutine(mb.DelayedCoroutine(delay, a));
    }
}

public class Buff : MonoBehaviour
{
    public void OnBuff()
    {
        StopAllCoroutines();
        Debug.Log("buffed!");
        this.RunDelayed(2f, () => {
            Debug.Log("debuffed!");
        });
    }
}