Fiery Confluence's 1-damage-to-each-creature mode kills Dragon's Rage Channeler before Delirium turns it into a 3/3 flyer, and the 2-damage-to-each-opponent modes let us race their clock while also answering the 1/1 Monk tokens from Cori-Steel Cutter's Flurry trigger (they die to 1 damage unless pumped by prowess or equipment). Shadowspear gives the single creature it equips +1/+1, trample, and lifelink, which helps offset their Lightning Bolt-heavy removal suite and race more efficiently, and its {1} ability can also strip hexproof and indestructible from the opponent's permanents until end of turn if needed. Sundering Eruption's land destruction is low-impact since Izzet Delver doesn't depend on a single key nonbasic land. Lavaspur Boots' ward {1} is weak protection against a deck full of free counterspells like Force of Will and Daze, which counter spells rather than target our permanents and so don't care about ward.