Gruul Basking Broodscale Combo leans on Eldrazi Temple and Ugin's Labyrinth to generate multiple mana from a single land, so Damping Sphere limits those lands to producing a single {C} instead of multiple mana and taxes their spells as they chain multiple threats in a turn. Molten Rain blows up one of their nonbasic lands (which make up most of their manabase) to slow their big mana plan and deals 2 extra damage to boot. Rain of Gore is low-impact here but Eidolon of the Great Revel is very risky against a deck full of cheap card-selection and ramp spells, so it comes out. Keep pressuring their life total early since this deck wants time to assemble its Eldrazi payoffs.