Crested Sunmare is a super interesting card from Hour of Devastation. It’s an enormously powerful threat if you can manage to consistently get triggers. It’s also a very interesting size for the format, given that the better removal spells are Abrade, Harnessed Lightning, and Grasp of Darkness, which all have a hard time dealing with a 5/5. The real problem for Crested Sunmare is finding a shell which can naturally maximize your ability to cast it and get a horse on the same turn. Given that lifegain is just a good thing to be doing in a format dominated by Zombies and Ramunap Red, Rooney56 may have found a great way to empower the Sunmare:

White-Black Lifegain - Hour of Devastation Standard | Rooney56, 5-0 Standard League

• Creatures (21)
• 1 Kalitas, Traitor of Ghet
• 4 Crested Sunmare
• 4 Glory-Bound Initiate
• 4 Lone Rider
• 4 Sunscourge Champion
• 4 Thraben Inspector

• Planeswalkers (4)
• 4 Gideon, Ally of Zendikar

• Instants (5)
• 1 Anguished Unmaking
• 4 Fatal Push

• Sorceries (1)
• 1 Declaration in Stone

• Enchantments (2)
• 2 Authority of the Consuls

• Artifacts (2)
• 2 Aethersphere Harvester

• Lands (25)
• 7 Plains
• 2 Ifnir Deadlands
• 4 Concealed Courtyard
• 4 Crypt of the Eternals
• 4 Shambling Vent
• 4 Shefet Dunes

• Sideboard (15)
• 3 Anguished Unmaking
• 1 Declaration in Stone
• 3 Fumigate
• 3 Solemnity
• 1 Sorin, Grim Nemesis
• 4 Warping Wail

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Rooney56 solves this problem by utilizing Glory-Bound Initiate and Aethersphere Harvester as cards that can attack very well and offset opposing attackers, particularly when backed up by Fatal Push to clear away the more threatening blockers. You also have Sunscourge Champion as an early roadblock that can gain you a substantial amount of life going into the late game. Further, you’ve got all manner of awesome ways to ensure that you maximize your Crested Sunmare triggers once they hit the battlefield. In particular, Crypt of the Eternals is a low-cost way to get a little extra life, while Authority of the Consuls can help you get extra Sunmare triggers on your opponent’s turn.

The biggest innovation in Rooney56’s build is the inclusion of a second payoff card for all slots in this deck dedicated to gaining life. Sure, the ability to keep pace with aggressive decks is great, but gaining life for its own sake usually isn’t good enough, and Crested Sunmare on its own isn’t a consistent reward. Enter Lone Rider. This whacky card from Eldritch Moon can end a game before it really gets started. How many aggro decks are prepared to deal with a huge, first striking, lifelinking threat?

If your metagame is primarily composed of decks on the more aggressive end of the spectrum, then this deck seems like a great way to punish them while not giving up your ability to play big threats in midrange and control mirrors. Gideon and Crested Sunmare are still monstrously powerful; you just have to make sure you can buy enough time that those cards get to actually take over the game.