Amulet Titan wants to assemble bounce-land and Amulet of Vigor value into an explosive Scapeshift or Primeval Titan turn, and Harbinger of the Seas shuts off their nonbasic lands like Urza's Saga, Simic Growth Chamber, and Gruul Turf, crippling their mana base and ramp engine. Mystical Dispute is a generic three-mana counter here since they run no blue spells, useful for stopping a key Scapeshift or Primeval Titan. Force of Negation and Counterspell remain your best tools to stop Scapeshift, while Counterspell also stops a Cultivator Colossus outright, so keep the full playset. Trim the clunky top-end Quantum Riddler and Tamiyo, Inquisitive Student since this matchup rewards proactive disruption of their mana engine over grinding card advantage.