Mainboard (60)
Instants (14)
Sorceries (4)
Artifacts (1)
Enchantments (16)
Gruul Goblins is a fast aggro deck that can kill before you assemble the Replenish combo, so the post-board plan focuses on buying time to stabilize. Meddling Mage naming Goblin Lackey shuts off their most explosive draws, while Exalted Angel provides a large lifelink blocker that quickly pulls you out of burn range and demands an answer. Tsabo's Web neutralizes Rishadan Port and Wasteland, which would otherwise strangle your mana and prevent you from going off. Decree of Silence and Mana Leak come out because Goblins dump their hand by turn two or three, making counterspells largely dead; one Frantic Search and one Seal of Cleansing are trimmed since the Seal has few targets and you need room for the stabilization package. Once the board is stabilized, Opalescence plus Parallax Wave still closes the game cleanly.
Mono-Blue Stiflenought wins by using Stifle to counter Phyrexian Dreadnought's sacrifice trigger, landing a free 12/12 trampler backed by a dense permission suite of Counterspell, Foil, Daze, and Thwart. Defense Grid is the linchpin of the sideboard plan — once it resolves, casting Replenish or Opalescence on your turn becomes nearly impossible for the opponent to interact with without spending significant mana they likely lack. Meddling Mage naming Stifle protects Parallax Wave's activated ability and Attunement's draw trigger from being countered mid-combo sequence, and can also name Counterspell to neutralize their most efficient hard counter. Seal of Cleansing comes out because the opponent has no meaningful enchantments or artifacts in the main deck, making it a near-blank. Mana Leak is too unreliable here given the opponent's 17 Islands and multiple free or pitch counterspells, so prioritizing the proactive disruption of Defense Grid and Meddling Mage is the correct trade-off.
Mono-Black Midrange's most dangerous threat to your gameplan is Withered Wretch, which can exile your enchantments and invalidate a Replenish entirely; bring in Hydroblast and Blue Elemental Blast to destroy it at instant speed before it activates, and they double as efficient answers to Hypnotic Specter and Knight of Stromgald. Meddling Mage naming Withered Wretch is your best proactive protection, or name Cabal Therapy if they're likely to flash it back repeatedly. Mana Leak is cut because Dark Ritual gives them burst mana to pay the tax easily, and the heavy discard suite (Duress, Cabal Therapy) strips counterspells from your hand before you can use them. Trim two Swords to Plowshares since Knight of Stromgald has protection from white and reduces the spell's targets, though keeping two handles Hypnotic Specter and Nantuko Shade. Retain most of your Seal of Cleansing suite because they board in Gloom and Dystopia — both enchantments that either tax your white and blue spells by three mana or force you to sacrifice your enchantments every upkeep, either of which can lock you out of the game.