This is a mirror-adjacent matchup versus a blue-black control/tempo deck full of blue spells (Counterspell, Preordain, Psychic Frog), so Mystical Dispute gets its full discount and becomes efficient interaction or a way to push through your own threats. Since Dress Down is already in the maindeck, bringing in a second copy adds redundancy to strip abilities off Psychic Frog or Orcish Bowmasters at instant speed while also cantripping. Lightning Bolt is a weak removal spell against their resilient 1/2s that grow (Psychic Frog gains counters) and doesn't answer planeswalkers like Kaito, Bane of Nightmares, so two copies come out for more targeted disruption.