This looks like it can end the game really quickly if gets going but I would personally play 24 lands and add 4x Vines of Vastwood to protect your creatures from removal.
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knight of cliffhaven, student of warfare, skywatcher adept, halimar wavewatch, corahelm commander. All among the best levelers imo.
unstable footing + earthquake in sideboard for kor firewalker.
no fetch lands? teetering peaks?
put in 4 bolts instead of flame slash. and you're going to want 4 of crumbling necropolis for sure and possible more dual lands. scalding tarn fetches blue and red. you have a bunch of options. If you're running those 3 colors you may as well be playing 4 sedraxis scepter's and maybe even a cruel ultimatium. sideboard = duress, deathmark, boom blade, essence scatter, negate, consuming vapors, pithing needle, you have a lot of options once again.
I'd take out the hackblades for 2 broodmate dragon and 2 siege-gang commander. Id also but Great Sable Stag in the sideboard, at least 2 of them.
You need an answer to Malakir Bloodwitch
Looks pretty good, I just don't like levelers at all and I like master and stag too much to not run them.