Boros Aggro runs a heavy nonbasic manabase (Inspiring Vantage, Sacred Foundry, Cavern of Souls, Multiversal Passage, Sunbillow Verge) so Sunspine Lynx's ETB damage trigger hits hard while also shutting down any incidental lifegain they might access. Thought-Stalker Warlock's menace helps trade with or pressure through their small early creatures like Voice of Victory while stripping a card to slow their curve. Stinging Vitriol's low damage mode is outclassed in a straight race, and Valley Flamecaller's bonus is less relevant since this matchup comes down to who runs out of resources first in a fast race. Prioritize racing and use Burst Lightning to answer their early threats like Momo and Sarkhan before they snowball.