UR Aggro's clock comes from cheap, evasive threats like Slickshot Show-Off and Elusive Otter, so Shoot the Sheriff cleanly answers their non-outlaw creatures at instant speed. Witherbloom Charm's destroy mode handles their small permanents or an Eddymurk Crab-style cheap threat, while Glorious Decay can hit their fliers for 4 damage, which kills most of their small flying bodies. The Misty Mountains Cold is far too slow against this tempo-aggro deck's clock, and Stir Up Trouble's extra cost is a liability when we need to be efficient, so both come out.