Dimir Midrange wins with card advantage engines like Kaito, Bane of Nightmares and Enduring Curiosity, so Duress strips key disruption or removal (including Kaito itself while it's still in hand) before it matters. Note that Duress can't take creatures such as Enduring Curiosity. Strategic Betrayal is a sorcery that makes them exile a creature of their own choice, so you don't pick their best one. It is best when they have few creatures on the battlefield, and it can't reliably deal with Kaito, who is only a creature during his controller's turn. It also exiles their graveyard as a small bonus. Erode comes out since many of their early threats are small merfolk/rats that your other removal handles fine, and Iron-Shield Elf is a weak blocker against their evasive value creatures. Keep Requiting Hex, as it still answers Dream Beavers, Spyglass Siren, and other cheap threats. Cool but Rude stays in as a looting and discard-damage engine rather than as removal.