Very nice deck. Here are a few suggestions. I don't think Nykthos, Shrine to Nyx would do much is this deck since it's multicolored and you have only 2 cards with devotion 2. I would highly suggest adding Ruric Thar, the Unbowed and Bow of Nylea . With only 5 non creature spells in your deck, Ruric will barely affect you. The Bow is very versatile; I've used each ability more than once and deathtouch is surprisingly effective, even in a fatty deck like this. Skarrg Guildmage could also do work in this deck. 6+ damage on turn 3 is nothing to scoff at.Gruul Charm would be a good sideboard choice.Finally, I would replace Slaughterhorn with Rubblebelt Maaka . The extra point of toughness is surprisingly useful and should you want to cast this as a creature spell, this deck should have no trouble getting to 3R by turn 3.

Just playtested this, lol... I managed to do 60 damage in one turn. Domri emblem + tons of creatures + Xenagos, God of Revels. New T2 record. Would be enough to kill three players.