As Protoss, you must use at least one (two, three ?) hallucinated unit in every attack.
I think Hallucinations are not used enough. The upgrade is cheap, fast and there's a lot of possibilities. Good players can utilize micro to get more out of the Hallucinations and this doesn't distrupt standard play so much, allowing more sucessful submission.
I wanted to restrict attacking when you have a significant ammount of hallucination but I don't now exactly how to put it. 1 hallucination for every sentry ? It would be pointless to have a 200/200 deathball with one hallucination in it.
P.S. The tags: IdrA, rage quit fit so good here :D