Seriously though, I think this will turn out very similar to the whole phione/manaphy relation. Some how with giratina, we recieve this thing with subpar/similar ivs. Which makes me think UU wall type thing. But then again, if it were programmed into the game wouldn't we know about it? If it is obtainable how would we get/use it?
Which then again makes me thinkg of zapmolcuno. Available in manga, but not in games, xD.
EDIT: SWChill, you are wrong. If it were available this gen, why wouldn't we see any sprites? If your going to say, " When you transfer to opal it turns into that thing. " I highly doubt this because again, we would have seen at least a sprite with stats. (for when battling on wifi, we aren't going to be seeing a blank screen... )
Plus it would be unfair for opal to not be able to use Giratina.
EDIT2: Now I'm thinking something along the lines off...
Thousands of billions of years ago there were these pokemon (serpentina)
but the world was in danger type of thing. So they called the "Leader" Giratina had saved the world, but with the cost of all its minions. So it hid in its labirntyh (Turnabck cave) only to come when the world is in danger once again.