Belcher is a fast, non-interactive combo deck aiming to resolve Goblin Charbelcher or Tameshi loops for lethal; Thoughtseize is our best tool, letting us strip their combo piece or a key protection spell (Disrupting Shoal, Force of Negation) on turn one before they can go off. Vexing Bauble counters any of their free-cost spells like Disrupting Shoal cast for its alternate cost of exiling a card, since no mana is spent, which is a real and relevant interaction against this exact deck. Thraben Charm's damage mode is irrelevant since they have essentially no creatures to kill, and Chthonian Nightmare does nothing against a deck with no meaningful graveyard or creature plan, so both are cut for proactive disruption.