Monday will kick off previews of Mirrodin Besieged as well as on various sites around the Internet, including this one! ManaNation will feature its exclusive preview card on Monday, taking part in the first day of spoilers for the upcoming set.
Until then, you can also see that Wizards has put up the Orb of Insights. Yes, plural. There is an Orb of Insight for each faction, one for Mirran cards, and one for Phyrexian.
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