UR Aggro fills the board with cheap creatures like Llanowar Elves and Spider Manifestation, most of which have 1 or 2 toughness, so Pyroclasm and Fire Magic (cast at Fira for {2}{R} to deal 2) are excellent sweepers here. Voice of Victory also shuts down their ability to hold up Spell Pierce on our turn, protecting our own development. Lost in the Maze only taps down a couple of threats and doesn't answer the deck's card advantage engine, while North Wind Avatar and a copy of Winternight Stories are too slow against this tempo strategy. Prioritize surviving to turn 4-5 where our bigger threats simply outclass their board.