Affinity's entire gameplan revolves around artifacts, so Deglamer answers their key threats like Myr Enforcer, Baleful Strix, or Utrom Monitor by shuffling them away, and Suplex can either exile any of those artifacts or deal 3 damage to a smaller creature. Breath Weapon deals 2 damage to each non-Dragon creature, which sweeps Baleful Strix, Glint Hawk, and Refurbished Familiar while your Avenging Hunter and Sagu Wildling survive as Dragons, though your own Arbor Elves will die too. Faerie Macabre stays in the sideboard: it costs {1}{B}{B}, which Gruul can't realistically cast, and exiling Blood Fountain or Ichor Wellspring from the graveyard denies nothing. Bannerhide Krushok and Rancor come out since this matchup is about efficiently answering their cheap artifact creatures rather than going over the top, and You Meet in a Tavern is too slow against their low curve. Prioritize removing Baleful Strix and Myr Enforcer, since those are the hardest threats for your ground creatures to profitably block.