Mardu Constellation!
I went into this metagame originally wanting to play Temur, but then I looked at the cards available to me.
Butcher of the Horde is kind of ridiculous with Athreos in play. Butcher is an awesome creature that only gets better with creatures in play to sacrifice to it, and with Athreos in play, we can get our cards back or bolt our opponent. The more I thought about this, the more I thought about synergy, and what creatures benefit the most from being able to be played multiple times over the course of a game, or even a turn?
The conclusion I came to was obviously Constellation. Triggering Constellation with Underworld Coinsmith and Doomwake Giant is awesome in conjunction with our threats being as big as they are. These two are also awesome targets for a bestowed Herald of Torment, especially since itself and Coinsmith are major sources of devotion for Athreos.
The deck has a lot of different options you can take, which I think is where it's power lies. Want to go on the offensive? Get some sac fodder for Butcher in your opening turns, Downfall, Banish, or Blight anything your opponent has to offer, and go to town! Want to go on the defense? Thoughtseize/Depise (if your looking for a budget alternative)/Brain Maggot your opponents hand to oblivion, set up Nyx-Fleece Rams until you get Doomwake mana, and just wrath their board with all the cheap enchantments you have available. A Read the Bones in the sideboard also helps this strategy.
I really like this deck because it's powerful, it's creative, it's got major synergy all around, and most importantly, there aren't any good board wipes in standard at the moment, making all these creature based strategies even better. The sideboard should be tuned to your meta, but I think that the options I have here are okay. Read the Bones for advantage, Magma Spray for something like rabblemaster or other small creatures, Erase for Jeskai Ascendancy, or gods or other enchantment creatures like Courser or Eidolon of Blossoms.
Playtest, +1, and enjoy!
