Mono-Blue Stiflenought wins by either landing a free Phyrexian Dreadnought (via Stifle) or countering everything you play while drawing through their deck with Gush and Portent. Chill is your best weapon here, taxing every blue spell by 2 mana and effectively shutting down their counter-magic and card draw engine — resolve it early and it often wins the game on its own. Defense Grid further punishes them on their turn, making it nearly impossible to hold up Counterspell and Daze simultaneously. Your removal suite (Diabolic Edict, Smother, Snuff Out) is largely dead against a deck that wins with a single indestructible 12/12, so trim the less impactful pieces while keeping Diabolic Edict in full as your primary answer to Dreadnought. Duress and Cabal Therapy are critical — strip Stifle before playing your threats and discard their counterspells before resolving Chill or Defense Grid.