Mono-Blue Terror plays no red cards, so Blue Elemental Blast and Hydroblast have no legal targets and stay in the sideboard. Their maindeck is also entirely blue with no artifacts, so those cards would do nothing here. Tolarian Terror and Cryptic Serpent get cheaper for every instant and sorcery in their graveyard, and their Mental Note, Thought Scour, Brainstorm and Ponder fill it quickly, so Nihil Spellbomb is a real answer: exiling their graveyard makes those threats much more expensive. Dispel gives us another way to counter their Counterspell, Dispel, Spell Pierce and instant cantrips like Brainstorm, Mental Note and Thought Scour, which are all instants (it can't hit sorceries like Ponder). Bender's Waterskin is a slow mana rock that doesn't affect the race, so trim it for the extra interaction. Focus on countering their Terror/Serpent before it resolves, since once online those threats are very hard to profitably block or race.