This is the mirror match against another Gruul Broodscale Combo deck, so it comes down to who assembles Eldrazi Temple/Urza's Saga into a threat first and who has the better disruption. Nature's Claim answers their Vexing Bauble or a resolved Blade of the Bloodchief cheaply, while Grafdigger's Cage disrupts their own Malevolent Rumble/graveyard recursion plans and can be very strong if you land it before they do. Since they're likely to bring in similar Trinisphere and Thief of Existence effects, prioritize speed and proactive threats over trying to out-grind them. Keep Unholy Heat and Walking Ballista in as flexible interaction against their Basking Broodscale and Glaring Fleshraker.

Izzet Prowess is a fast aggressive deck full of one-toughness threats like Dragon's Rage Channeler and Monastery Swiftspear, making Firespout an excellent Sorcery-speed sweeper that can wipe their whole board for one mana with Grove of the Burnwillows or Stomping Ground. The extra Unholy Heat is efficient, cheap removal that answers their early plays before Cori-Steel Cutter or Expressive Iteration takes over. Cut the slow artifact utility pieces that don't affect the board fast enough against this clock. Be aware they'll bring in Consign to Memory and extra Unholy Heat of their own, so try to play your threats in ways that punish a missed counterspell.

Boros Energy floods the board with cheap creatures like Solitude and grinds with Wrath of the Skies and Price of Freedom, so Firespout comes in as a Sorcery that can wipe their early board before they stabilize. The extra Unholy Heat give you more efficient removal against their low-toughness threats, while Vexing Bauble taxes their glut of one-mana interaction and removal spells. Cut the narrow artifact answers and Walking Ballista, which is too slow and too easily picked off by their removal suite. Play around Wrath of God and Wrath of the Skies by not overextending into open mana.