Affinity's entire board is almost all artifact spells: Myr Enforcer, Refurbished Familiar, Utrom Monitor, Baleful Strix, Cryogen Relic, Giant's Boulder, Blood Fountain and Nihil Spellbomb are all counterable by Annul for one blue mana (Thoughtcast is a sorcery, not an artifact, and Glint Hawk is a white Bird creature, not an artifact, so neither is a legal target). Bringing in all 4 Annul is the single best adjustment in this matchup. Arms of Hadar's -2/-2 sweeps their fragile small artifact creatures like Refurbished Familiar and Baleful Strix. Keep Dispel in since Reckoner's Bargain and Dispatch are both instants; cut slower selection pieces like Faerie Seer, Augur of Bolas and Plunder the Trollshaws since Affinity has no red cards, so Blue Elemental Blast and Hydroblast stay in the sideboard.