Azban is fairly obvious and you have the option to splash both red and blue, although the mana is easier in blue and it has a powerful morph. I'd like to splash for Kolaghan but ultimately I think it's just a little too greedy.
I think that Hardened Scales is basically not a card, even with as many +1/+1 counters as this deck has. The rest is me choosing better creatures (flyers and blockers). Not sure why you missed Incremental Growth from your build.
1 Ainok Bond-Kin
2 Brave the Sands
1 Pressure Point
1 Valorous Stance
1 Kill Shot
1 Sandblast
1 Alabaster Kirin
1 Citadel Siege
1 Sage's Reverie
1 Smite the Monstrous
1 Great-Horn Krushok
Blue (9)
1 Force Away
1 Frost Walker
2 Wetland Sambar
1 Whisk Away
1 Mistfire Adept
1 Mistfire Weaver
1 Aven Surveyor
1 Enhanced Awareness
Black (14)
1 Molting Snakeskin
1 Ancestral Vengeance
1 Battle Brawler
1 Douse in Gloom
1 Bellowing Saddlebrute
1 Mer-Ek Nightblade
1 Fearsome Awakening
1 Krumar Bond-Kin
1 Reach of Shadows
2 Rotting Mastodon
1 Sibsig Host
1 Gurmag Angler
1 Sibsig Muckdraggers
1 Collateral Damage
1 Mardu Scout
1 Temur Battle Rage
1 Act of Treason
1 Bathe in Dragonfire
1 Gore Swine
1 Howl of the Horde
2 Swift Kick
1 Lightning Shrieker
1 Ainok Tracker
Green (23)
1 Hardened Scales
1 Warden of the First Tree
2 Ainok Guide
2 Archers' Parapet
1 Feed the Clan
1 Smoke Teller
1 Whisperer of the Wilds
1 Abzan Beastmaster
1 Alpine Grizzly
2 Frontier Mastodon
1 Scout the Borders
1 Dragonscale Boon
1 Fruit of the First Tree
1 Sudden Reclamation
1 Incremental Growth
1 Pine Walker
1 Sagu Archer
1 Tusked Colossodon
1 Sandsteppe Mastodon
1 Woolly Loxodon
1 Ankle Shanker
1 Cunning Strike
1 Kolaghan, the Storm's Fury
1 Abomination of Gudul
Colorless (2)
1 Briber's Purse
1 Jeskai Banner
Lands (9)
1 Bloodstained Mire
2 Blossoming Sands
1 Dismal Backwater
1 Jungle Hollow
1 Opulent Palace
1 Rugged Highlands
1 Scoured Barrens
1 Thornwood Falls
Rares/Mythics (8)
1 Warden of the First Tree
1 Hardened Scales
1 Sandsteppe Mastodon
1 Citadel Siege
1 Howl of the Horde
1 Ankle Shanker
1 Kolaghan, the Storm's Fury
1 Bloodstained Mire
And this is the deck I came up with:
1 Abzan Beastmaster
1 Ainok Bond-Kin
2 Ainok Guide
1 Alabaster Kirin
1 Bellowing Saddlebrute
1 Gurmag Angler
1 Krumar Bond-Kin
1 Mer-Ek Nightblade
1 Pine Walker
1 Sandsteppe Mastodon
1 Warden of the First Tree
1 Whisperer of the Wilds
1 Woolly Loxodon
1 Citadel Siege
1 Douse in Gloom
1 Dragonscale Boon
1 Hardened Scales
1 Kill Shot
1 Reach of Shadows
1 Sandblast
1 Smite the Monstrous
1 Valorous Stance
5 Forest
4 Plains
3 Swamp
2 Blossoming Sands
1 Jungle Hollow
1 Opulent Palace
1 Scoured Barrens
Was pretty happy with Abzan in this pool, but there was definitely some Mardu possibilities as well.
Last cut: 1 Douse in Gloom, 1 Ainok Guide
1 Ainok Bond-Kin
1 Ainok Guide
2 Archers' Parapet
1 Whisperer of the Wilds
1 Abzan Beastmaster
1 Pine Walker
1 Abomination of Gudul
1 Mistfire Weaver
1 Woolly Loxodon
1 Alabaster Kirin
1 Mer-Ek Nightblade
1 Sandsteppe Mastodon
1 Kill Shot
1 Sandblast
1 Citadel Siege
1 Smite the Monstrous
1 Dragonscale Boon
1 Incremental Growth
1 Reach of Shadows
2 Blossoming Sands
1 Dismal Backwater
1 Jungle Hollow
1 Opulent Palace
1 Scoured Barrens
1 Thornwood Falls
5 Plains
5 Forest
1 Swamp
W 3+5 for 7 cards
B 4+1 for 2 cards
G 5+5 for 9 cards
U 3+0
Curve
1 c
2 cccccs
3 cccccss
4 ccsss
5 ss
6+c
Differences from you:
1 Hardened Scales
1 Douse in Gloom
1 Ainok Guide
1 Bellowing Saddlebrute
1 Gurmag Angler
1 Krumar Bond-Kin
1 Incremental Growth
2 Archers' Parapet
1 Abomination of Gudul
1 Mistfire Weaver
1 Dismal Backwater
I think that Hardened Scales is basically not a card, even with as many +1/+1 counters as this deck has. The rest is me choosing better creatures (flyers and blockers). Not sure why you missed Incremental Growth from your build.