Meltdown for X=1 destroys Amulet of Vigor (mana value 1) before it can untap their bounce lands and fuel the ramp engine, and it also sweeps up any Urza's Saga Construct tokens, which have mana value 0. Vexing Bauble is narrow, but it counters Summoner's Pact, which is cast for {0} with no mana spent, so they can't use it to fetch a green creature. Thought Scour and Sink into Stupor do little against a deck racing to assemble Scapeshift or Primeval Titan, so they're cut for proactive hate. Thoughtseize remains critical to strip their key combo pieces before they resolve.