Izzet Delver is a fast tempo deck built around Dragon's Rage Channeler and Murktide Regent backed by Lightning Bolt and Wasteland, so Barrowgoyf gives us a resilient deathtouch, lifelink blocker that stabilizes against their aggressive creatures while growing from the shared graveyards. Firespout cast for R sweeps their non-flying creatures like Dragon's Rage Channeler for 3 damage, which is enough to kill it outright. Sink into Stupor and Giant's Boulder are too passive and slow against a deck threatening fast clocks, so we cut them for more proactive, resilient answers. Force of Will stays maxed to fight through their own Daze and Force of Will protecting Murktide Regent.