Decklist: http://i.imgur.com/ZiTuSns.png
Last season I’ve been experimenting with a Koan of Horns deck after reaching S-rank and somehow unpacking two Koans. The deck seems to work extremely well against Spellhai and Cassyva which is commonly known as Reva’s counter.
Explanations
Reva Eventide x1 For early game you want to summon a bunch of heartseekers to create pressure and force your opponent to react. Some may argue that Kaleos is better for Gore Horns but early game Kaleos has no synergy with this deck.
Inner Focus x3 Staple as it synergises with fox, panddo, beholder but personally I like to save it once I got gorehorns.
Mana Vortex x3 Mostly for card draw and occasionally you can get a seven mana Koan out. We don’t run much high cost spells so either save it for Magi or just use it when you have a bad hand
Healing Mystic x3 I found this deck struggles against aggro and Spellhai and six health makes a big difference, I found tusk boar to be useless as it doesn’t contest board and I won’t run killing edge or mirror meld. You can also heal your fox or panddo for more value.
Phoenix Fire x3 All around removal, a staple in almost every Songhai deck. Also kills heartseekers buffed with killing edge so that’s a plus.
Xho x3 A filler two drop that also gives you tools which you can replace if you don’t need. The one mana discount is huge and I’ve won games by the opponent not expecting pre-nerf seven mana spiral off Xho.
Battle Panddo x3 Besides making your opponent panic or waste dispels which they should be using on magi and fox, it also acts as an AOE which threatens heartseekers and abyssal crawlers. This helps greatly against Spellhai and Cassyva as it kills ooz on its own as well as making Reva and Cassyva think twice about using their BBS. We don’t run deathstrike as one to one synergy is not what we want.
Ki Beholder x2 Good for delaying threats as well as being a threat on its own. It’s a two-of simply because it’s useless when your opponent is close and putting pressure down. We also don’t run killing edge and inner focus is better used on our other minions.
Lantern Fox x3 If you don’t run this in Songhai I don’t know why you’re playing that faction. It creates pressure and forces removal unless they want you to have a hand full of fires.
Onyx Bear Seal x3 Against Songhai use it on their Four Winds or Foxes. Against Cassyva use it on basically any big threat they drop unless it’s Juggernaut and you have Lightbender in hand. The amount of tempo you gain is good enough that you can win simply on the fact you removed a Klaxon or Revenant with a three mana spell. Cassyva also has no means of buffing the panddo. The fact that there’s still a minion on the board means you will almost always be able to run twin strike.
Spelljammer x3 Good card draw if you ever run out of cards. Your opponent usually panics and removes it without thinking.
Twin Strike x3 A good cantrip as well as removal. Synergy with Onyx Bear Seal as you can cast it essentially on one minion. This might dilute the value of this card but you should be able to phoenix fire to keep the board clean and use your Battle Panddo and Fox to maintain board balance.
Four Winds Magi x3 Healing is always welcome when you’re running a late game deck, you have enough spells to activate it. It doesn’t do that much for us but if your opponent leaves it up they’re still going to have a bad time.
Lightbender x2 Noone expects a REVA to run this card let alone dispel. I chose this over shroud due to its 3/3 body and because we want as much value as possible from one card this is why all our cards are decent on our own. Your opponent usually won’t hesitate to allow you to get a huge Lightbender off as they don’t expect you to run it.
Koan Of Horns x2 The cornerstone of this deck. Noone expects it but by the time you cast it’s already too late for them. However, if need to use removal on a big threat or dispel something, you should do that first as by using this card you are getting rid of your Lightbenders and Magis which could get you killed if you’re low.
Guide
Another gimmick of this deck is simply no one plays around the cards you are running. Half of your deck is Spellhai and Xho and Mystic could simply be tech cards. No one plays around Panddo or Lightbender in Reva either. Be careful or overcommitting when summoning Gore Horns as frostburn and obliterate would swing the value game back to the opponent so much that you might aswell concede.
Noted exceptions
Ancestral Divination It’s useless if you haven’t use Koan of Horns and a dead card is not part of our game plan. If we don’t win the early value game we won’t be able to spam Gore Horns.
Chakri Avatar Our goal isn’t to burst opponents and we don’t have that many low cost spells to be able to buff it for trading.
Tusk Boar While this card is good for sniping ranged minions and contesting mana tiles, it doesn’t give you board presence and you end up replacing it after it returns to your hand anyways.
So yeah have fun and try to improve it if you can 
I created this deck when S-rank was flooded with Revas and Cassyvas teching against Revas. My deck had an almost 90% win rate against those decks but due to those tech cards, it loses it’s near insta-win again Magmar and against Lyonar, which is already a bad matchup for Spellhai, if you don’t get deathstrike zeal of Xho and cast it on Battle Panddo you’re probably going to lose.