“Mono-Blue Stiflenought wins by cheating Phyrexian Dreadnought into play as a 12/12 trampler on turn one by using Stifle or Vision Charm to counter its 'sacrifice creatures with total power 12 or greater' triggered ability. The deck protects this threat and its combo pieces with a dense suite of free and cheap counterspells (Counterspell, Foil, Daze, Thwart, Misdirection), while cantrips and card draw (Opt, Portent, Gush, Impulse) provide the consistency needed to assemble the two-card combo quickly. The strategy is essentially a tempo-combo hybrid: land a 12/12 on turn one and then protect it long enough to kill the opponent in two attack steps.”
Missing sideboard cards? The full 15-card sideboard runs about $46.01.
Buy sideboard on ManapoolThis is the mirror, so the game is about who assembles the Dreadnought/Stifle-or-Vision-Charm combo first and who protects it better. Annul counters the Phyrexian Dreadnought spell itself or an opposing Powder Keg, giving a clean proactive answer that the maindeck lacks. Chain of Vapor can bounce a resolved Dreadnought (triggering the sacrifice ability again) or bounce their own Island to rebuy Daze-style tempo, and the extra copy adds flexibility. Flash of Insight, Peek, and Thwart are the weakest cantrip/counter redundancies and are trimmed slightly since the matchup rewards efficient answers over card selection. Keep all core combo pieces and the bulk of the counterspell suite untouched since the mirror is still won by resolving your own Dreadnought first and protecting it.
Azorius Replenish is entirely built around enchantments (Attunement, Opalescence, Parallax Wave, Replenish, Decree of Silence), making Annul a premium answer that can counter any of their key combo pieces for a single mana. Chain of Vapor adds another way to interact with a resolved Opalescence or Parallax Wave before the lock turn fully sets up. Flash of Insight, Peek, and Thwart are trimmed slightly since proactive, cheap interaction with their combo pieces is more valuable than card selection in a matchup decided by who assembles their game plan first. Keep the full Counterspell/Foil/Daze/Misdirection suite since you need to both protect your own Dreadnought and disrupt their Replenish turn.
Terrageddon's manabase is loaded with nonbasics (Gemstone Mine, Wasteland, Windswept Heath, Treetop Village, Rishadan Port, Mox Diamond's color-fixing), making Back to Basics extremely punishing since it can lock them out of casting spells after Armageddon resets the board. Essence Flare provides a cheap way to add pressure outside the Dreadnought combo since Swords to Plowshares answers Dreadnought cleanly and you want a backup threat. Daze is weaker here since you don't want to sacrifice tempo before an Armageddon turn, and Flash of Insight/Peek are cut since card selection matters less than resilience to land destruction. Keep Stifle and Vision Charm as your core combo engine, and hold Counterspell/Foil for their Swords to Plowshares or Armageddon.