Ruby Storm wins by chaining rituals like Seething Song and Desperate Ritual into a game-ending burst, so Mesmeric Fiend's hand disruption can strip a key combo piece such as Big Score or Seize the Storm before they go off. Quirion Ranger is low-impact here since you need proactive disruption rather than incremental mana efficiency against a combo deck trying to win outright. Flaring Pain stays in the sideboard: it only stops damage from being prevented, and Ruby Storm has no damage prevention, so it does nothing in this matchup. Prioritize deploying Mesmeric Fiend early to see their hand and take their best piece.