Ruby Storm is almost entirely red and colorless rituals and card advantage, so Mystical Dispute is a cheap, efficient way to stop a key Pyretic Ritual chain or a game-ending Past in Flames even though most of their spells aren't blue themselves, since the generic {2}{U} cost is still affordable. Force of Negation stays in at full count, since countering a Past in Flames or a lethal Grapeshot for free on their turn is one of the best things our deck can do against this matchup. Wistfulness is a weak card here since the opponent runs few artifacts or enchantments worth exiling and its card-draw mode is too slow against a deck that can kill out of nowhere, so it is the safest cut to make room for additional interaction.