Gruul Ramp wants to accelerate into big threats like Primordial Pachyderm, Avenging Hunter, and Bramble Wurm, so we need to close the game before they stabilize with their large bodies. Cast into the Fire can pick off small mana creatures like Arbor Elf or an Eldrazi Spawn token from Eldrazi Repurposer, slowing their ramp plan. Relic of Progenitus disrupts their Malevolent Rumble graveyard filling and any recursive value, though it won't stop their permanent-based ramp like Wild Growth or Utopia Sprawl. Inventor's Axe and an extra Chain Lightning are cut in favor of proactive disruption, since we want to race and stunt their mana rather than grind.