Welcome, initiates! If you wish to undergo the Trial of Knowledge, you must seek every hidden whisper of truth in the turning of pages and understand every subtle shift in the currents of the wind. You must open your mind and let it fill the shape of reality as a graceful cat flows to fit exactly into a sink. You must meditate upon the difference between their owners' hands and their owner's hand.
If you're pressed for time, I guess you can just read this article.
Remember how Kaladesh and Aether Revolt were nice, simple updates? Well, buckle up! This update has a massive overhaul to split cards, naming cards, putting counters, and not casting spells. I promise Hour of Devastation will return to less turbulent changes. I mean, with that set name, how could it possibly be tumultuous?
Look for the Comprehensive Rules to be updated soon here.