Mono Black Aggro fields a swarm of small creatures (Bloodghast, Stitcher's Supplier, Dark Matter Manipulator, Gifted Aetherborn), so Pyroclasm can clear several of them at once, even if Bloodghast can return via landfall. It is not one-sided, though: it also kills our own Monastery Swiftspear, Soul-Scar Mage and Emberheart Challenger, so time it carefully. Flowstone Infusion kills their x/2-or-smaller creatures outright (Bloodghast, Stitcher's Supplier, Dark Matter Manipulator, Liliana the Repentant), but it will not kill Gray Merchant of Asphodel (2/4) or Gifted Aetherborn (2/3). Ramunap Ruins' life payment is dangerous against an aggressive deck, and Monstrous Rage is less needed when we can simply remove their blockers with burn. Keep Burst Lightning and Reckless Rage as flexible interaction against 3-toughness threats like Gifted Aetherborn and Baron Helmut Zemo. Note that neither kills a 5-toughness creature like Sheoldred, the Apocalypse (4/5) or an Overlord of the Balemurk (5/5).