UR Aggro is built on blue and red spells, and Flashfreeze only counters red or green ones. That still makes it a good answer to their red threats and burn: Burst Lightning, Slickshot Show-Off, Impractical Joke, Wild Ride and Vibrant Outburst. It can't touch their mono-blue spells such as Flow State or Sleight of Hand, so save it for the red cards. Qarsi Revenant's flying deathtouch lifelink body blocks profitably against Slickshot Show-Off and helps stabilize our life total against their burn plan. Duress is weak against a deck full of cheap cantrips and creatures rather than discardable bombs, since it can only take noncreature, nonland cards. Winternight Stories is too slow against this aggressive clock, so both come out for more resilient, proactive answers.