Izzet Delver is a fast tempo deck that grows Dragon's Rage Channeler and Murktide Regent while backing them up with Daze, Force of Will, and Lightning Bolt, so you need cheap interaction that doesn't cost tempo. Into the Flood Maw answers a flying Murktide Regent or a delirium'd Dragon's Rage Channeler at instant speed for a single mana, resetting their clock without taxing your limited mana. Golgari Thug's 1/1 body is irrelevant on defense against their evasive threats and doesn't contribute enough to your racing plan, so cut it for the cheap bounce spell. This matchup is primarily a race, so prioritize assembling your kill as fast as possible.