Prismatic Ending can exile Lion's Eye Diamond or other cheap permanents central to their Doomsday pile before they go off. Spell Pierce taxes their Doomsday itself or a key cantrip like Ponder when they're tapped out setting up, which is often enough to blow them out since Doomsday decks run on thin mana. We trim slower creatures for cheap, proactive disruption because this matchup is a race to either pressure their low life total or disrupt the combo turn; Swords to Plowshares remains relevant against Thassa's Oracle.