First of all, how DID Mephiles get a hold of it in the first place?
This is not explained.
And if you're still admiring the Omega Paradox Blog Post that's been made, well, if you think about it, a future Omega from the point before Mephiles Phase 1 jumps into the present time. Okay, sounds about right. But how could he have sealed Shadow? With having jumped back into the present, this means that the timeline has been altered, the events never came to pass, and Shadow was never sealed away. But how Omega keeps records (or, artificial memories) of himself in sealing Shadow in the first, by all means, how!? He jumped through time to the present. There is not future Omega in Crisis City, or Flame Core, anymore!
Once again, Sega messed up.