Annul is a cheap, relevant answer in this matchup: it counters Animate Dead as they try to reanimate their key combo piece, and it can also hit Survival of the Fittest, which is an enchantment, along with artifact creatures like Phyrexian Devourer and Triskelion. It can't stop Unearth, which is a sorcery, so rely on your general counterspells for that. Stifle, already in your core, can counter the Hermit Druid activated ability outright before it mills their library, which is the single best interaction point in the matchup. Thwart is clunky when you need to react immediately to a Hermit Druid activation, so cut it for the cheaper, more relevant Annul. Hold up mana and counterspells on their turn rather than tapping out to deploy your own threats, since this opponent can win out of nowhere once Hermit Druid resolves.