Dimir Excruciator is a mirror-ish matchup full of small-to-medium creatures (Seasoned Cryomancer, Superior Spider-Man, Overlord of the Balemurk) that Day of Black Sun can wipe for a low X while leaving our own bigger threats untouched. Null Summoner adds another discard-style effect to fight through their Duress-heavy disruption suite and can later cast whatever it exiles. Winternight Stories and Awaken the Honored Dead are too slow in a mirror where both decks are racing card advantage and removal efficiency.