Missing sideboard cards? The full 15-card sideboard runs about $296.
Buy sideboard on ManapoolHullbreacher punishes their cantrip-heavy draws off Brainstorm, Ponder, and their Clue-type effects, converting every extra card into Treasure for us while slowing their engine. The extra One Ring gives us another resilient card advantage engine that dodges their removal-light disruption suite (mostly Thoughtseize and Fatal Push target creatures, not artifacts). Sink into Stupor and Eldrazi Confluence are too clunky against a deck that plays efficient cheap interaction and wants us proactive; Lorien Revealed is replaced by a free Force effect we actually want to hold up. Keep Force of Will and Force of Negation at full count since their Daze/Force of Will will try to protect Murktide Regent and flipped threats.
Barrowgoyf is a great blocker and lifelink/deathtouch threat that stabilizes against their wide token board of Cat tokens and Ocelot Pride triggers, trading up with anything due to deathtouch. Dismember cleanly answers Ajani, Nacatl Pariah (a 1/2 or transformed planeswalker threat) or Guide of Souls for cheap, both of which generate significant value if left unchecked. Sink into Stupor and Eldrazi Confluence are too slow and card-disadvantageous against a deck that goes wide and recoups tempo losses quickly, while Lorien Revealed doesn't affect the board in a matchup where we need blockers and removal. Keep Giant's Boulder and Kozilek's Command as primary removal since they answer anything on the opposing board for value.
Hullbreacher is devastating against Aluren and Show and Tell since it turns their extra draws from Atraxa, Grand Unifier and Stock Up into Treasure instead of cards, and it also disrupts their Aluren engine loops that rely on drawing extra cards off creature chains. Tormod's Crypt can proactively strip their graveyard before they cast Acererak the Archlich's escape-adjacent payoffs or use their Nethergoyf-style self-mill pieces indirectly tied into card advantage (note: mostly a hedge, bring in only if you see graveyard synergies). Sink into Stupor is too slow versus a combo deck that just needs to resolve Show and Tell or Aluren once, and Lorien Revealed is too passive when we need to be proactive with countermagic and threats. Keep all Force of Will/Force of Negation copies since stopping Show and Tell or Aluren is our best interaction.