Boros Energy is full of small creatures (Ragavan, Guide of Souls, Voice of Victory tokens) that Unholy Heat answers cleanly, especially once delirium turns it into a 6-damage spell. Magebane Lizard punishes their noncreature-spell-heavy plan (Galvanic Discharge, Thraben Charm, Fable) by pinging them for every spell cast, which adds up fast against a deck that casts multiple cheap spells per turn. Street Wraith's swampwalk is irrelevant since the opponent plays no Swamps, and the extra card selection from Mishra's Bauble matters less than removal and a proactive clock here. Watch out for their Blood Moon, which can strand your black mana if you're not careful with sequencing.