It's no secret that Miracles has had a stranglehold on the Legacy format for quite some time now. It's consistently the most-played deck and always one of the best-performing decks in the tournament.
The natural response to the omnipresence of Miracles is a rebirth of attrition-based midrange decks in Legacy, most notably Shardless Sultai. That deck has certainly risen from its low point to become a serious contender in the format, but for some people, drawing three cards just may not be enough.
A few years ago, there was a Four-Color Cascade deck that used Bloodbraid Elf in addition to Shardless Agent to both apply more pressure and ratchet up the card advantage a notch. Today's deck takes that idea to the extreme with one of my favorite cards of all time: Ninja of the Deep Hours.
By itself it's a card draw engine that costs significant tempo when you put it onto the battlefield via ninjitsu. When your Ninja of the Deep Hours is removed immediately it can be devastating, but if you return a creature with an enters-the-battlefield ability you gain immediate card advantage. Against most decks you'd worry about the tempo loss, but Miracles is quite poor at punishing you on tempo.
Every creature but Deathrite Shaman here generates card advantage, as does the powerful Hymn to Tourach. When paired with the three best answers in Legacy — Force of Will, Lightning Bolt, and Abrupt Decay — you have a deck that can answer any potential trump card from the opponent while grinding them into a fine paste.
With so much emphasis put on beating Miracles, you may worry that this deck will be behind against the rest of the format, but Shardless Sultai has always matched up well against Delver variants because of its efficient removal and the presence of Baleful Strix. And against combo, you have access to Force of Will and plenty of discard between Hymn to Tourach and the sideboard copies of Thoughtseize. Eternal Witness and Shardless Agent let you establish a clock while giving you more reliable access to your disruption regardless of matchup.
It's unclear whether Ninja of the Deep Hours is better than Bloodbraid Elf in this shell, but the upside is certainly there. Drawing two cards a turn in any format will end games in a hurry, and the fact that one-for-one removal is so poor against the rest of the deck mitigates the risk of having your Ninja killed before it connects.
Fewer Legacy tournaments mean the format will evolve more slowly and the return of attrition-based midrange decks has been a long time coming. Hopefully they stick around for a while, because I for one am sick of Sensei's Divining Top.