Izzet Phoenix wants to fill its graveyard and chain cheap spells to rebuy Arclight Phoenix (3/2 flying) for free, so Scorching Shot reliably kills it and any Picklock Prankster (1/3) before it can protect the combo. Spell Pierce is excellent proactive disruption on early turns when they're trying to set up Artist's Talent or cast a cheap cantrip to enable Phoenix, and it dodges their low land count strategy of playing around counterspells. Boomerang Basics does little against a deck that doesn't rely on sticking many permanents besides Arclight Phoenix, which simply returns from the graveyard anyway. Race them by pressuring their life total early, since your prowess creatures punish them for tapping out on cantrips just as much as their own deck does to you.