Well, after countless Showdown battles, I can say that WoW+Shadow Sneak+Outrage+Roar is excellent, and is usually a safe way for me to open up. I cannot even begin to count how many people have switched in Xerneas on Outrage (often to their surprise that it cancels, often without confusion) and go Geomancy with their Power Herb, only to be trollishly switched out. In short, it DOES in fact work. And well, too.
Yeah, an unexpected Roar can be good against less experienced players who spam Geomancy Xerneas, but people who know what they're doing would just take the free kill with Moonblast. It's hard to find a Gira-O set that isn't Ho-oh or Defog bait, two things you definitely don't want against better players.

