Boros Aggro is a fast, flying-heavy deck with Momo, Friendly Flier, Voice of Victory, and dragons like Magmatic Hellkite and Nova Hellkite, so we need cheap blockers and a sweeper rather than slow value creatures. Qarsi Revenant's flying, deathtouch, lifelink body is excellent defensively against their fliers and buys life back against their burn, while Day of Black Sun at X=3 or X=4 wipes Momo, Sarkhan, Dragon Ascendant, Voice of Victory, and Clarion Conqueror while costing us little since our own curve tops above those numbers in key cards. Overlord of the Balemurk's impending cost makes it a non-blocker for five turns if cast cheaply, which is far too slow against this aggressive clock, so it comes out. Duress is weak since Boros brings almost no removal or key discardable answers and instead wants to race; prioritize keeping blockers and life total high.