Jund Wildfire's primary threats are Krark-Clan Shaman, which can sacrifice artifacts to ping all your faeries to death, and Gixian Infiltrator, which is difficult to chump-block with 1/1s due to menace. Hydroblast does double duty here: it counters Cleansing Wildfire (a red sorcery that fuels their engine) and cleanly destroys Krark-Clan Shaman (a red creature) before it can wreck your board. Arms of Hadar is a sorcery that sweeps their small threats — Gixian Infiltrator, Refurbished Familiar, and Krark-Clan Shaman all have power 2 or less — but use it only when you haven't overextended your own faeries, since it will hit them too. We cut Gurmag Angler because they run Nihil Spellbomb in the main and Faerie Macabre in the sideboard, making delve unreliable; Murmuring Mystic replaces it as a resilient threat that generates chump-blockers off your instants and sorceries. Abandon Attachments and Spell Pierce have no meaningful targets in this matchup and come out to make room.