Annul is strong here, cheaply countering Opalescence, Parallax Wave, Decree of Silence, Attunement, or Seal of Cleansing before the opponent can lock the game up. It cannot counter Replenish, which is a sorcery, so you'll need your other counters for that. Your maindeck Chain of Vapor already bounces Opalescence or an animated enchantment post-Replenish, so keep it in and cut the slower Powder Keg instead. The extra Chain of Vapor in the sideboard is redundant with the one you're keeping. Thwart is a clunky 4-mana counter that costs you board development; cut it for the more efficient, on-target Annul. Prioritize countering Replenish itself with Counterspell, Foil, or your other counters, or stopping the Attunement/Frantic Search setup, over racing with Dreadnought if the lock pieces are already down.