Stiflenought's whole plan hinges on using Stifle to counter Phyrexian Dreadnought's own sacrifice trigger, so Pyroblast is excellent tech here — it can counter their Stifle itself (letting the Dreadnought's trigger resolve and forcing them to sacrifice it away) or simply counter Counterspell, Foil, or Daze to protect your own combo. Rushing River returns a resolved Dreadnought to their hand, forcing them to recast it and re-risk the sacrifice trigger, buying you a full extra turn. Tsabo's Web and City of Traitors come out since this opponent runs no vulnerable tapped utility lands and you need your mana untapped and available to fight through their dense counterspell suite. Keep Defense Grid and Tangle Wire in, since Defense Grid taxes their instant-speed interaction on your turn and Tangle Wire slows their explosive starts.