Consign to Memory costs only {U} and counters a triggered ability (or a colorless spell, though they have none). That makes it a cheap answer to Tamiyo's attack trigger that investigates, Phelia's attack trigger, and Quantum Riddler's enter-the-battlefield draw. It also keeps your mana efficient when you're trying to deploy Show and Tell or Sneak Attack under pressure from their Daze and Force of Will. Spell Pierce is a weaker fit since this deck plays efficiently and can often find the extra {2}, and you'd rather keep mana up for your own plan than tax theirs. Core pieces like Show and Tell, Sneak Attack, and your Force of Will suite stay in since this matchup is still fundamentally a race to resolve your payoff before their Swords to Plowshares and Stifle disrupt it.