I think he is thinking of the Necro I quest where ideally you have a minimum of 4 people. Each one to stand on a pressure plate at the same time. I remember duoing that one before multi boxing and hirelings ever existed. I forget the name of it.
Also the swim in Delera's part... 3 was it? Been so long. But I can't remember if that was required or not. I don't think you could truly solo that one.