Mystical Dispute is efficient interaction against a deck with no blue spells to discount it, but it's still a solid {2}{U} counter against key pieces like Karn, the Great Creator, Ugin, Eye of the Storms, or their large Eldrazi threats. Consign to Memory comes in as cheap interaction for a colorless matchup, countering key colorless spells or triggered abilities while our removal suite (Prismatic Ending, Solitude) handles their threats on the board by exiling them. Day's Undoing symmetrically refills their hand with more threats and is not favorable when we're ahead on card quality, and Consult the Star Charts is clunky against prison elements like Chalice of the Void (which counters 2-mana spells) and Trinisphere (which increases the cost of spells under 3 mana to 3 mana), so both are trimmed.