Mono Red Rally is a race deck that can goldfish kills on turn three, so your plan is to go under them with a fast heroic creature backed by Ethereal Armor or Cartouche of Solidarity rather than trying to out-grind them. Obsidian Acolyte comes in to protect your threats from Galvanic Blast and Lightning Bolt by granting protection from red, turning off their entire removal suite at a critical moment. Standard Bearer is a powerful disruptive tool that redirects all targeted spells — including your own — to itself, effectively shutting down their ability to target your heroes; note that you must still trigger your own heroic creatures first before Standard Bearer enters, or sequence around it carefully. Spirit Link is cut because the lifegain is too slow against their goldfish speed, and Skyward Spider is too passive and defensive for a matchup where you need to apply pressure immediately. Prioritize getting a heroic creature into play on turn one and layering enchantments as fast as possible — if you can resolve Ethereal Armor on a protected creature, Mono Red struggles to break through.