Amulet Titan needs Scapeshift to find its bounce-lands and Urza's Saga package, and Gaddock Teeg shuts off Scapeshift outright since it's a noncreature spell with mana value 4. Force of Vigor is a free way to blow up Urza's Saga before it comes online, and it can also destroy Amulet of Vigor itself once it resolves. We cut our more matchup-narrow removal since Amulet Titan is trying to combo off rather than attack with creatures.