Eldrazi leans heavily on Chalice of the Void to shut off our cheap cantrips and interaction, so Meltdown (even X=0 destroys a Chalice, since it has mana value 0 on the battlefield) and Ratchet Bomb give us ways to clear it along with Lotus Petal. Spell Pierce is weak here since Eldrazi threats like Thought-Knot Seer and Reality Smasher are colorless creatures that dodge it entirely, and Into the Flood Maw is less appealing against a deck full of big, resilient bodies we'd rather kill than bounce. Force of Will and Daze remain important to protect our own plan since Eldrazi's Thought-Knot Seer will strip our hand if left unanswered. Lightning Bolt is valuable to answer creatures like Glaring Fleshraker and the 3/3 Eldrazi Linebreaker before they snowball, while Unholy Heat only kills 2-toughness creatures like Glaring Fleshraker unless we have Delirium.